Do you love math? Love numbers? Love the thrill of problem-solving and the quiet satisfaction of finding that one right answer? If so, these math riddles in mathematics are just for you! 1. Riddle: How do you make the number 7 even without addition, subtraction, multiplication, or division? Answer: Drop the "S". 2. Riddle: Can you write down eight eights so that they add up to one thousand? Answer: 888 + 88 + 8 + 8 + 8 = 1000. 3. Riddle: How can you take 2 from 5 and leave 4? Answer: F I V E Remove the 2 letters F and E from five and you have IV. 4. Riddle: How many sides does a circle have? Answer: Two. The inside and the outside. 5. Riddle: How many times can you subtract the number 5 from 25? Answer: Once, because after you subtract 5 from 25 it becomes 20. 6. Riddle: When John was six years old he hammered a nail into his favorite tree to mark his height. Ten years later at age sixteen, John returned to see how much higher the nail was. If the tree grew by five centimeters each year, how much higher would the nail be? Answer: The nail would be at the same height since trees grow at their tops. 7. Riddle: I am four times as old as my daughter. In 20 years time I shall be twice as old as her. How old are we now? Answer: I am 40 and my daughter is 10. 8. Riddle: What did one math book say to the other math book? Answer: Do you want to hear my problems? 9. Riddle: Lily is a lilypad in a small pond. Lilly doubles her size each day, On the 20th day she covers the whole pond. On what day was Lily half the size of the pond? Answer: Day 19, it's not 10 because on day 20 she doubled from day 19, so 19 must be half the size of the pond. 10. Riddle: There is a clothing store in Bartlesville. The owner has devised his own method of pricing items. A vest costs $20, socks cost $25, a tie costs $15 and a blouse costs $30. Using the method, how much would a pair of underwear cost? Answer: $45. The pricing method consists of charging $5 for each letter required to spell the item. 11. Riddle: One is to three as three is to five and five is to four and four is the magic number. What is the pattern? Answer: One has three letters in the word three has five letters in it five has four letters and four has four letters in it (if you try more numbers they will always come back to the number four: so four is the magic number) 12. Riddle: If a boy blows 18 bubbles, Then pops 6 eats 7 and then He pops 5 and blows 1. How many are left? Answer: 1. 13. Riddle: The ages of a father and son add up to 66. The father's age is the son's age reversed. How old could they be? (3 possible solutions). Answer: 51 and 15. 42 and 24. 60 and 06. 14. Riddle: What did the triangle say to the circle? Answer: You’re pointless. 15. Riddle: What two whole, positive numbers that have a one-digit answer when multiplied and a two-digit answer when added? Answer: 1 and 9. 16. Riddle: You want to boil a two-minute egg. If you only have a three-minute timer (hourglass), a four-minute timer and a five-minute timer, how can you boil the egg for only two minutes? Answer: Once the water is boiling, turn the three-minute timer and five-minute timer over. When the three-minute timer runs out, put the egg in the boiling water. When the five-minute timer runs out, two minutes have elapsed and it is time take the egg out of the water. You don't need the four-minute timer for this riddle. 17. Riddle: 81 x 9 = 801. What must you do to make the this equation true? Answer: Turn it upside down. 108 = 6 x 18. 18. Riddle: How much will a 38° angle measure when looked at under a microscope that magnifies ten times? Answer: It will still be 38°. 19. Riddle: 1=5, 2=15, 3=215, 4=3215, 5=? Answer: 5=1, because 1=5. 20. Riddle: In a certain city, 5% of all the persons in town have unlisted phone numbers. If you select 100 names at random from that city's phone directory, how many people selected will have unlisted phone numbers? Answer: None. If their names are in the phone directory, they do not have unlisted phone numbers! 21. Riddle: How can you make the following equation true by drawing only one straight line: 5+5+5=550? Can you figure it out? Answer: Draw a line on the first plus sign that turns it into a 4! The equation then becomes true: 545+5=550. You could also change the equal symbol to a crossed out equal symbol which means "not equal to". 22. Riddle: What did the little lobster get on its math test? Answer: Sea-plus. 23. Riddle: If you're 8 feet away from a door and with each move you advance half the distance to the door. How many moves will it take to reach the door? Answer: Infinity! Technically you will never reach the door, as you can only move half the distance, no matter how small. 24. Riddle: How old is your son? asked a man to his neighbour. My son is five times as old as my daughter and my wife is five times as old as my son. Iam twice as old as my wife whereas my grandmother, who is celebrating her eighty-first birthday is as old as all of us put togeather. How old is the man's son? Answer: Five. 25. Riddle: I am a three digit number. My tens digit is five more than my ones digit. My hundreds digit is eight less than my tens digit. What number am I? Answer: Number 194. 26. Riddle: You have 6 eggs.You break 2, cook 2 and you eat 2 eggs. How many do you have left? Answer: 4. The 2 you break are the ones you cook, which are the ones you eat. 27. Riddle: A sphere has three, a circle has two, and a point has zero. What is it? Answer: Dimensions. 28. Riddle: If 4+2=26, 8+1=79 and 6+5=111. Then, what is 7+3? Answer: 410.4+2=26 is because 4-2=2 and 4+2=6,so it is 26. Therefore, 7-3=4 and 7+3=10(410). 29. Riddle: Why is it easier to count cows than sheep? Answer: You can use a cowculator. 30. Riddle: A tree doubled in height each year until it reached its maximum height over the course of ten years. How many years did it take for the tree to reach half its maximum height? Answer: Nine Years. 31. Riddle: Find the four digit number in which the first digit is one fourth of the last digit, the second digit is 6 times the first digit, and the third digit is the second digit plus 3. What is it? Answer: 1694. 32. Riddle: In a stable there are men and horses. In all, there are 22 heads and 72 feet. How many men and how many horses are in the stable? Answer: 14 horses and 8 men. 14x4 plus 8x2 = 72 feet. 33. Riddle: Take two numbers, such that the square of the first, plus the square of the second, shall equal 8; while the first, plus the product of the first and second, shall equal 6. What are the two numbers? Answer: 2 and 2. 34. Riddle: Something very extraordinary happened on the 6th of May, 1978 at 12:34 a.m. What was it? Answer: At that moment, the time and day could be written as: 12:34, 5/6/78. 35. Riddle: What do mathematics teachers like to eat? Answer: Pi. 36. Riddle: What happened to the plant in the math classroom? Answer: It grew square roots, of course. 37. Riddle: When my father was 31 I was 8. Now he is twice as old as me. How old am I? Answer: The difference in age is 23 years, so I must be 23 if my father is twice as old as me. 38. Riddle: What is the most useful instrument in a mathematics teacher's tool kit? Answer: Multi-pilers! 39. Riddle: What do you call two math friends? Answer: Algebros!! 40. Riddle: What is the next number in the sequence? 2, 3, 5, 9, 17, _ Answer: 33. The pattern: Double the previous number and subtract 1. 41. Riddle: What did one math book say to another? Answer: I have so many problems. 42. Riddle: If three cats catch three mice in three minutes, how many cats would be needed to catch 100 mice in 100 minutes? Answer: The same three cats would do. Since these three cats are averaging one mouse per minute, given 100 minutes, the cats could catch 100 mice. 43. Riddle: Take eight small sticks, four of which are half the length of the other four. How can you make three equal squares out of the sticks? Answer: Use the longer four sticks to be sharing sides between the squares and at the end their should be three intertwined squares. 44. Riddle: A man is walking down a road with a basket of eggs. As he is walking he meets someone who buys one-half of his eggs plus one-half of an egg. He walks a little further and meets another person who buys one-half of his eggs plus one-half of an egg. After proceeding further he meets another person who buys one-half of his eggs plus one half an egg. At this point he has sold all of his eggs, and he never broke an egg. How many eggs did the man have to start with? Answer: 7 eggs. The first person bought one half of his eggs plus one half an egg (3 1/2 + 1/2 = 4 eggs) This left him 3 eggs. The second person bought one-half of his eggs plus one half an egg, (1 1/2 + 1/2 = 2 eggs) leaving the man 1 egg. The last person bought one-half of his eggs plus one-half an egg, (1/2 + 1/2 = 1 egg) leaving no eggs. 45. Riddle: What is the next number in the series? 7,645 5,764 4,576... Answer: 6,457. The last digit is moved to the front to make the next number. 46. Riddle: A new medical building containing 100 offices had just been completed. Mark was hired to paint the numbers 1 to 100 on the doors. How many times will Mark have to paint the number nine? Answer: The answer is 20! 9, 19, 29, 39, 49, 59, 69, 79, 89, 90, 91, 92, 93, 94, 95, 96, 97, 98, 99. 47. Riddle: What arithmetic symbol can we place between 2 and 3 to make a number greater than 2 but less than 3? Answer: A decimal point. 48. Riddle: Taking that internship in a remote mountain lab might not have been the best idea. Pulling that lever with the skull symbol just to see what it did probably wasn't so smart either. But now is not the time for regrets because you need to get away from these mutant zombies...fast. Can you use math to get you and your friends over the bridge before the zombies arrive? Alex Gendler shows how. Answer: At first it might seem like no matter what you do, you're just a minute or two short of time, but there is a way. The key is to minimize the time wasted by the two slowest people by having them cross together. And because you'll need to make a couple of return trips with the lantern, you'll want to have the fastest people available to do so. So, you and the lab assistant quickly run across with the lantern, though you have to slow down a bit to match her pace. After two minutes, both of you are across, and you, as the quickest, run back with the lantern. Only three minutes have passed. So far, so good. Now comes the hard part. The professor and the janitor take the lantern and cross together. This takes them ten minutes since the janitor has to slow down for the old professor who keeps muttering that he probably shouldn't have given the zombies night vision. By the time they're across, there are only four minutes left, and you're still stuck on the wrong side of the bridge. But remember, the lab assistant has been waiting on the other side, and she's the second fastest of the group. So she grabs the lantern from the professor and runs back across to you. Now with only two minutes left, the two of you make the final crossing. As you step on the far side of the gorge, you cut the ropes and collapse the bridge behind you, just in the nick of time. 49. Riddle: If seven people meet each other and each shakes hands only once with each of the others, how many handshakes will there have been? Answer: Twenty one. Most people would think there were 42 handshakes. The first person shakes the hand of 6 others, the second person shakes the hand of 5 remaining people, the third person shakes the hand of 4 remaining people, the fourth person shakes the hand of 3 remaining people, the 5th person shakes the hand of 2 remaining people and the sixth person shakes the hand of 1 remaining person. 6+5+4+3+2+1=21 50. Riddle: I am a two-digit number. All my digits are even. No two digits are the same. None of my digits are prime numbers. I am not a multiple of ten. My tens digit is bigger than my other numbers. If you followed all the previous steps, there should be three options remaining the number is the option where if you add all the digits it's exactly in the middle (in how big the number is) of all the other options with their digits added together. What number am I? Answer: If you followed all the steps apart from the last one there will be three options remaining: 64, 84, and 86. You then had to add up the digits, 64=6+4=10, 84=8+4=12, and 86=8+6=14. Finally, you then had to take up the middle biggest number (12) and put it back as it was before the digits were added together and your answer should be 84. 51. Riddle: Adored by few, Feared and hated by many. Mistress of the entire universal reason, Master in the art of numbers. Some may have solved many of your mysteries, But there still much of them to find. What are they? Answer: Mathematics. 52. Riddle: I am a three-digit number. All of my digits are prime. One of the numbers is even. Each of my numbers are used only once. The total of my first and last digits equals 10. The total of my first two digits equals 5. Answer: This one is fairly easy if you use elimination if you follow all the first 5 steps you get three options: 525, 327, and 723 but if you followed the last step you would reach your answer. The answer was 327. 53. Riddle: If someone says to you, "I'll bet you $1 that if you give me $2, I will give you $3 in return", would this be a good bet for you to accept? Answer: No. This is a situation where you lose even if you win. Assuming the other person is being wise, they would take your $2 and say, "I lose", and give you $1 in return. You win the bet, but you're out $1. 54. Riddle: The distance from the Earth to the Sun is about 100 million miles. The speed of light is 186,000 miles per second, and light takes eight minutes to reach the Earth from the Sun. Let's say the Sun rose at 6am this morning, and that by some freak of physics the speed of light is suddenly doubled to 372,000 miles a second. What time will the Sun rise tomorrow? Answer: 6am again. After all, what diffrence does the speed of light make to the answer? It's irrelevant- only the speed of the roation of the Earth matters here. 55. Riddle: A bottle costs a dollar more than a cork. Together they cost 110 cents. How much does the bottle cost and how much does the cork cost? Answer: The right answer is that the bottle costs 105 cents, and the cork costs 5 cents. 56. Riddle: Jim was examining an angle measuring 14 and 1/2 degrees, using his magnifying glass that magnifies everything two times. Under the glass, how large would that angle measure? Answer: 14 and 1/2 degrees. Explanation, angles remain constant when magnified. A square has 4-90 degree corners, if you zoom in (magnify) a square, it's still a square. 57. Riddle: The head of a whale is six feet long; his tail is as long as his head and half his body, and his body is half of his whole length. How long is the whale? Answer: Forty-eight feet. 58. Riddle: Place three piles of matches on a table, one with 11 matches, the second with 7, and the third with 6. You are to move matches so that each pile holds 8 matches. You may add to any pile only as many matches as it already contains. All the matches must come from one other pile. For example, if a pile holds 6 matches, you may add 6 to it, no more or less. You have three moves. How can you do it? Answer: First pile to second; second to third; third to first: Pile Initial number First move Second move Third move First 11 11-7=4 4 4+4=8 Second 7 7+7=14 14-6=8 8 Third 6 6 6+6=12 12-4=8 59. Riddle: In a pond, there are some flowers with some bees hovering over them. If both the following statements are true: 1. If each bee lands on a flower, one bee doesn't get a flower. 2. If two bees share each flower, there is one flower left out. How many flowers and bees are there? Answer: 4 bees and 3 flowers. 60. Riddle: King Tut died 120 years after King Eros was born. Their combined age when they died was 100 years. King Eros died in the year 40 B.C. In what year was King Tut born? Answer: King Tut was born in 20 B.C. There were 120 years between the birth of King Eros and the death of King Tut, but since their ages amounted to only 100 years, there must have been 20 years when neither existed. This would be a period between the death of King Eros, 40 B.C., and the birth of King Tut, 20 B.C. 61. Riddle: There are two numbers whose product added to the sum of their squares is 109, and the difference of whose squares is 24. What are the two numbers? Answer: 5 and 7. (5)² = 25(7)² = 49(5x7)+25+49=10949-25=24 62. Riddle: At a children's party, 10 kids had juice, 8 kids had cake, and 6 kids had juice and cake. How many kids were there at the party? Answer: Tweleve kids. Six kids had juice and cake, leaving two out of the cake eaters that didn't have juice. As there were ten juicers, there must be twelve kids in total. 63. Riddle: Robert and David played several golf matches against each other in a week. They played for a pizza at each match, but no pizzas were purchased until the end of the week. If at any time Robert and David had the same number of wins, those pizzas were canceled. Robert won four matches (but no pizzas), and David won three pizzas. How many rounds of golf were played? Answer: Eleven, David won 7 matches, 4 to cancel out Robert's 4 wins, and 3 more to win the pizzas. 64. Riddle: There is a certain club which is for men only. There are 600 men who belong to this club and 5% of these men wear one earring. Of the other 95% membership, half wear two earrings and the other half wear none. How many earrings are being worn in this club? Answer: Six hundred. We know that 5%, or 30 of the men are wearing one earring. Of the other 95%, or 570, we know that half are wearing two earrings and the other half none. This is the same as if they all wore one. 65. Riddle: Two schoolgirls were traveling from the city to a dacha (summer cottage) on an electric train. "I notice," one of the girls said "that the dacha trains coming in the opposite direction pass us every 5 minutes. What do you think-how many dacha trains arrive in the city in an hour, given equal speeds in both directions?" "Twelve, of course," the other girl answered, "because 60 divided by 5 equals 12." The first girl did not agree. What do you think? Answer: If the girls had been on a standing train, the first girl's calculations would have been correct, but their train was moving. It took 5 minutes to meet a second train, but then it took the second train 5 more minutes to reach where the girls met the first train. So the time between trains is 10 minutes, not 5, and only 6 trains per hour arrive in the city. 66. Riddle: Can you combine plus signs and five 2's to get 28? Can you combine plus signs and eight 8's to get 1,000? Answer: 22+2+2+2=28; 888+88+8+8+8=1,000 67. Riddle: Janie's friends were chipping in to buy her a wedding shower present. At first, 10 friends chipped in, but 2 of them dropped out. Each of the 8 had to chip in another dollar to bring the amount back up. How much money did they plan to collect? Answer: $40 (10 at $4, or 8 at $5). 68. Riddle: Eight years ago, Bill was eight times the age of his son Bill Jr. Today, if you add their ages together, they add up to 52. How old are Bill and his son? Answer: Bill is 40, and Bill Jr. is 12. 69. Riddle: Three matches are sitting on a table. Without adding another make for three matches four. You are not allowed to break any of the matches. How can this be done? Answer: Shape the 3 matches into a roman numeral four. 70. Riddle: I am a place, in a state. I am an answer to a math problem. The math problem is: To get a cube, you multiply something by 6. What do you multiply by? Answer: You Times Square! 71. Riddle: A nonstop train leaves Moscow for Leningrad at 60 mph. Another nonstop train leaves Leningrad for Moscow at 40 mph. How far apart are the trains 1 hour before they pass each other? Answer: 100 miles (60+40) 72. Riddle: One fourth of the population of a newly discovered planet have 4 legs. The rest have two legs. There are 60 legs total. How big is the population of the newly discovered planet? Answer: 24. 73. Riddle: There is a creature which could double its size every day. So, if the creature is put in a tank then it will fill the tank in 10 days. How many days would it take for the creature to fill 1/2 and 1/4 of the tank? Answer: 9 days to fill 1/2 and 8 days to fill 1/4 of the tank. If the creature fills the tank in 10 days and it doubles every day, on the ninth day it would fill 1/2 the tank. Thus on the 8th day it will fill 1/4 of tank. 74. Riddle: How can you measure nine minutes with have two hourglasses, one four minute and one seven minute? Answer: Turn over both hourglasses at once. When the four-minute hourglass runs out, turn it over. When the seven-minute hourglass runs out, turn it over. When the four-minute timer runs out this time (eight minutes have elapsed), the seven-minute hourglass has been running for one minute. Now turn over the seven minute timer back over. When the timer runs out, nine minutes have elapsed. 75. Riddle: Three point one four, one five nine two six five, three five eight nine... What am I? Answer: Pi - π. 76. Riddle: Place three matches on a table. Tell a friend to add two more matches to make eight. How can this be done? Answer: Add two matches to make a roman numeral eight. 77. Riddle: A boy has as many sisters as brothers, but each sister has only half as many sisters as brothers. How many brothers and sisters are there in the family? Answer: Four brothers and three sisters. 78. Riddle: A 300 ft. train is traveling 300 ft. per minute must travel through a 300 ft. long tunnel. How long will it take the train to travel through the tunnel? Answer: Two minutes. It takes the front of the train one minute and the rest of the train will take two minutes to clear the tunnel. 79. Riddle: If two's company and three's a crowd, what are four and five? Answer: Four and five is nine. 80. Riddle: What is significant about 3661 seconds past midnight on 1st January 2001? Answer: The time and date will be 01:01:01 on 01/01/01. 81. Riddle: Tara has $29.00 dollars. She bought 4 coloring books that cost $3.00 each, 4 boxes of Crayola crayons that cost $2.00 each. She spends the rest of her money on markers. How much money did she spend on markers? Answer: She spent $9.00 on markers. 82. Riddle: A frog fell into a well 12 feet deep. He could jump 3 feet, but every time he jumped 3 feet, he fell back 2 feet. How many times did he have to jump to get out of the well? Answer: The tenth jump took him out. (On the tenth jump he reached 13 feet and was out.) 83. Riddle: Tom volunteered to be the chief organizer for the world's tether ball championships. There were 657 contestants from around the world. The tournament was set up whereby the winner would advance and the loser would be eliminated. Since there was an odd number of participants, the initial pairing leaves one player out. That player gets a bye and automatically advances to the next round. How many matches will Tom have to schedule to determine the tether ball champion? Answer: 656 matches will be needed. 84. Riddle: A certain number has three digits. The sum of the three digits equals 36 times this number. Seven times the left digit plus 9 is equal to 5 times the sum of the two other digits. 8 times the second digit minus 9 is equal to the sum of the first and third. What is the number? Answer: This one is fairly easy - 324 is the answer. 85. Riddle: You have 14 brown socks, 14 blue socks and 14 black socks in your sock drawer. How many socks must you remove (without looking to be sure) to have a matched pair? Answer: Four. You will have a pair of one color or another. 86. Riddle: David is throwing Robert a surprise birthday party but he has to stay within his budget. He spent half of his money plus $2.00 on the cake. Half of what he had left plus $2.00 was spent on balloons and streamers. Then he spent half of what he had left plus $1.00 on candy. Now he is out of money, how much did he start with? Answer: This one is best solved working backwards, the last part David spent half of what was left plus $1.00 on candy and then was out of money. That means he must have spent $2.00 on Candy as $1.00 was half of what he had using the same logic backwards: $2.00 on candy $6.00 on Balloons and Streamers $12.00 on the cake Total of $20.00. 87. Riddle: Why are 1999 ten pound notes worth more than 1993 ten pound notes? Answer: Because there are more of them! 88. Riddle: What is the 4 digit number in which the first digit is one-fifth of the last, and the second and third digits are the last digit multiplied by 3? Answer: 1155. 89. Riddle: A hundred stones are placed, in a straight line, a yard distant from each other. How many yards must a person walk, who undertakes to pick them up, and place them in a basket stationed one yard from the first stone? Answer: In solving this question it is clear that to pick up the first stone and put it into the basket, the person must walk two yards, one in going for the stone and another in returning with it; that for the second stone he must walk four yards, and so on increasing by two as far as the hundredth, when he must walk two hundred yards, so that the sum total will be the product of 202 multiplied by 50, or 10,100 yards. If any one does not see why we multiply 202 by 50 in getting the answer, we refer him to his arithmetic. 90. Riddle: Farmer Brown came to town with some watermelons. He sold half of them plus half a melon, and found that he had one whole melon left. How many melons did he take to town? Answer: Three melons! 91. Riddle: Two hours ago it was as long after one o'clock in the afternoon as it was before one o'clock in the morning. What time is it now? Answer: It would be 9:00 pm. There are 12 hours between 1:00 pm and 1:00 am and half of that is six hours. Half-way between would be 7 o'clock. Two hours later it would be 9:00 o'clock. 92. Riddle: You and your friend are trapped in a space prison on an alien planet. The alien warden decides to give you and your friend a chance at freedom. He states that your friend shall be allowed to temporarily leave your cell and try to escape through an electric gate guarded by a 3-number passcode. If your friend answers incorrectly or says anything but the final answer, your friend will be thrown back in the prison. A computer will then tell your friend 4 clues if requested. If this passcode is properly answered, you and your friend shall be freed. You are then blindfolded and your friend leaves. You hear your friend walk down one of the numbered hallways to the gate. Your friend asks for the first clue. A voice answers, "The numbers are in ascending order so that the number is greater than or equal to the number before it." Your friend asks for the second clue. The voice says, "The product of the 3 numbers is 36." Your friend asks for the third clue. The voice says, "The sum of the numbers is the number of the hallway you entered." Your friend pauses for a moment and thinks. Your friend then asks for the fourth and final clue. The voice says, "The largest number only appears once in the code." You hear a beep. You hear your cell door swing open. You are free! What was the code? Answer: 2,2,9 93. Riddle: If place 1 cake of soap on a pan of a scale and 3/4 cake of soap and a 3/4-pound weight on the other, the pans balance. How much does a cake of soap weigh? Answer: Since 1/4 cake weighs 3/4 pound, and entire cake weighs 3 pounds. 94. Riddle: If 10 bags of jelly beans and 6 licorice sticks cost $1, and 10 licorice sticks and 6 jelly bean bags cost 92 cents. How much does one licorice stick cost? Answer: 5 cents. Jelly bean bags cost 7 cents. 95. Riddle: A half is a third of it. What is it? Answer: 1 1/2. 96. Riddle: When completed in 1889 the Eiffel Tower was something of a sensation. Designed by the French engineer Alexandre-Gustave Eiffel its height is 492 feet plus half its own height. How high is the eiffel tower? Answer: 984 feet. 97. Riddle: Joe has ten coins totaling $1.19. From these coins, he cannot make exact change for a dollar, half-dollar, quarter, dime, or nickel. What are the coins? Answer: A half-dollar, a quarter, four dimes, and four pennies. 98. Riddle: Walking home one day, you take a short cut along the train tracks. The tracks cross a narrow bridge over a deep gorge. At the point you are 3/8 of the way across the bridge, you hear the train whistle somewhere behind you. You charge across the bridge, and jump off the track as the train is about to run you down. As it happens, if you had gone the other way, you would have reached safety just before being run over as well. If you can run ten miles per hour, how fast is the train moving? Answer: The train is moving at 40 miles per hour. Imagine that a friend is walking with you. When the train whistle blows, you head away from the train, he heads toward it. When he reaches safety, you will be 6/8 (or 3/4)of the way across the bridge, and the train will have just reached the bridge. For the train to cross 4/4 of the bridge in the time you cross the remaining 1/4, the train must be moving four times your speed. 99. Riddle: A woman went into a bank to cash an insurance refund check. By mistake the teller gave her dollars for cents and cents for dollars. She put the money in her purse but accidentally dropped a nickel on the floor. When she got home, she found that she had exactly twice the amount of the check she had cashed. She didn't have any money in her wallet before going to the bank. What was the exact amount of that check? Answer: The amount must have been $31.63. She received $63.31. After she dropped a nickel there would remain the sum of $63.26, which is twice the amount of the check. 100. Riddle: Twelve flags stand equidistant along the track at the stadium. The runners start at the first flag. A runner reaches the eighth flag 8 seconds after he starts. If he runs at an even speed, how many seconds does he need altogether to reach the twelfth flag? Answer: Not 12 seconds. There are 7 segments from the first flag tot the eighth, and 11 from the first to the twelfth. He runs each segment in 8/7 seconds; therefore, 11 segments take 88/7= 12 4/7 seconds.