A riddle problem is a question or statement intentionally phrased so as to require ingenuity in ascertaining its answer or meaning, typically presented as a game.  Below is a list of the past problem of the week riddles in descending chronological order.

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.
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.
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.
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?
Riddle: If the day before yesterday is the 23rd, then what is the day after tomorrow?
Riddle: Robert and David were preparing to have a water balloon fight. "No Fair" cried Robert, "You have 3 times as many as I do!" David said "Fine!" and gave Robert 10 more balloons. "Still not fair!" argued Robert, "You still have twice as many as I do." How many more balloons must David give Robert for them to have the same number?
Answer: David must give Robert another 20 water balloons, giving them each 60. Robert started with 30 water balloons and David with 90.