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Riddle:

Suppose you want to send in the mail a valuable object to a friend. You have a box which is big enough to hold the object. The box has a locking ring which is large enough to have a lock attached and you have several locks with keys. However, your friend does not have the key to any lock that you have. You cannot send the key in an unlocked box since it may be stolen or copied. How do you send the valuable object, locked, to your friend - so it may be opened by your friend?

Answer:

Send the box with a lock attached and locked. Your friend attaches his or her own lock and sends the box back to you. You remove your lock and send it back to your friend. Your friend may then remove the lock she or he put on and open the box.

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Riddle:

In 2000, a 40-year-old doctor told his son that when a little boy he decided to be a doctor by seeing a internet web site about performing a heart transplant on a puppy with a defective heart so that the puppy would live a normal life. I then thought that I would be a doctor so that I could help people in a similar way. What is the defect in this story?

Answer:

The internet did not exist when the doctor was a little boy.

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Riddle:

What is the next 3 letters in this riddle? o t t f f s s _ _ _

Answer:

e n t They represent the first letter when writing the numbers one thru ten.

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Riddle:

In a contest, four fruits (an apple, a banana, an orange, and a pear) have been placed in four closed boxes (one fruit per box). People may guess which fruit is in which box. 123 people participate in the contest. When the boxes are opened, it turns out that 43 people have guessed none of the fruits correctly, 39 people have guessed one fruit correctly, and 31 people have guessed two fruits correctly.

The Question: How many people have guessed three fruits correctly, and how many people have guessed four fruits correctly?

Answer:

It is not possible to guess only three fruits correctly: the fourth fruit is then correct too! So nobody has guessed three fruits correctly and 123-43-39-31 = 10 people have guessed four fruits correctly.

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Riddle:

You can use me to stop,

You take me to smoke;

Not only do I stop, But I am a stop,

And the result of pool's first stroke.

What am I?

Answer:

Brake/ Break

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Riddle:

A boy presses a side of a blue pencil to a side of a yellow pencil, holding both pencils vertically. One inch of the pressed side of the blue pencil, measuring from its lower end, is smeared with paint. The yellow pencil is held steady while the boy slides the blue pencil down 1 inch, continueing to press it against the yellow one. He returns the blue pencil to its former position, then again it slides down 1 inch. He continues until he has lowered the blue pencil 5 times and raised it 5 times- 10 moves in all.

Supposed that during this time the paint neither dries nor diminishes in quantity. How many inches of each pencil will be sneared with paint after the tenth move?

 

Answer:

At the start, 1inch of the yellow pencil gets smeared with wet paint. As the blue pencil is moved downward, a second inch of the blue pencils smears a second inch of the yellow pencil.

Each pair of down and up movesof the blue pencil smears 1 more inch of each pencil. 5 pairs of moves will smear 5 inches. This together with the initial inch, makes 6 inches for each pencil.

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Riddle:

Not far off shore a ship stands with a rope ladder hanging over her side. The rope has 10 rungs. The distance between each rung is 12 inches. The lowest rung touches the water. The ocean is calm. Because of the incoming tide, the surface of the water rises 4 inches per hour. How soon will the water cover the third rung from the top rung of the rope ladder?

Answer:

When a problem deals with a physical phenonmenon, the phenonmenon should be considered as well as the numbers given. As the water rises, so does the rope ladder. The water will never cover the rung.

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Riddle:

Can you divide the watch face with 2 straight lines so that the sums of the sums of the numbers in each part are equal? 

Answer:

The sum of the numbers on the watch face is 78. If the two lines cross, there must be 4 equal parts, but 78 is not divisible by 4. Then the lines do not cross, giving three parts with the sum of 26 each. Once you see the pairs on the face that add to 13(12+1,11+2, and so far) the answer will be easy to find.

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Riddle:

A watchmaker was telephoned urgently to make a house call to replace the broken hands on a clock. He was sik so he sent his apprentice.

The apprentice was thorough. When he finished inspecting the clock it was dark. Assuming his work was done, he attached the new hands and set the clock by his pocket watch. It was sic o'clock, so he set the big hand at the 12 and the little hand at the 6.

The apprectice returned, but soon the telephone rang. He picked up to his angry client:

"You didn't do the job right. The clock shows the wrong time."

Surprised he hurried back. He found the clock showing not much past eight. He handed is watch to the client and showed her that her clock was not even one second late. The client had to agree.

Early the nect morning, the client telephoned to say the clock has apparently gone berserk, hands were moving around the clock at will. The apprentice again rushed over, the clock showed a little past seven. After checking his watch he yelled:

"You are making fun of me! Your clock shows the right time!"

Have you figured out whats going on?

Answer:

As the problem says the apprentice mixed up the hands so that the minute hand was short and the hour hand was long.

The first time the apprentice returned to the client was about 2 hours and 10 minutes after he had set the clock at six.The long had moved olny from twelve to a little past two. The little made two whole circles and an additional 10 minutes. Thus the clock showed the correct time.

The next day around 7:o5 a.m.he came a second time,13 hours and 15 minutes after he had set the clock for six. The long had, acting as the hour hand,covered 13 hours to reach 1. The short hand made 13 full circles and 5 minutes, reaching 7, So the clock showed the correct time again.

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Riddle:

The title of the problem tells you how to approach these four questions.

(A).  A bus leaves Moscow for Tula at noon. An hour later a cyclist leaves Tula for mosco, moving slower than the bus. When the bus and cyclist meet, which one of the two will be farther from Moscow?

(B). Which is worth more: a pound of $10 gold peices or half a pound of $20 gold pieces?

(C). At six o'clock the wall clock struck 6 times. Checking with my watch, I noticed the time between the first and last strokes was 30 seconds. How long will the clock take to strike 12 at midnight?

(D). Three swallows fly outward from a point. When will they all be on the same plane in space?

Now check the answers. Did you fall into any of the traps which lurk in these simple problems?

Answer:

(A). Neither

(B). A pound of metal is always more than half a pound of the same metal.

(C). Six strokes took 30 seconds, therefore 12 strokes will take 60 seconds. But when the clock struck six, there were only 5 intervals between strokes, and each interval was 30/5=6 seconds. Between the first and twelfth strokes there will be 11 intervals of 6 seconds each, therefore 12 strokes will take 66 seconds.

(D). There is always a plane that contains any 3 points 

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