Riddle: An empty bus pulls up to a stop and 10 people get on. At the next stop 5 people get off and twice as many people get on as at the first stop. At the third stop 25 get off.
How many people are on the bus at this point?
Answer: Just 1, the driver.
Riddle: The London Racetrack needs to submit its 3 fastest horses to the Kentucky Derby out of 25 horses. However, all of their information was lost and they don't know any of the horse's times. Similarly, they all look identical so they can't remember who's fastest.
They can only race 5 horses at once, so what is the fewest number of races they can conduct to find the 3 fastest horses?
Answer: 7 races are required.
First you divide the 25 horses into 5 groups of 5. You conduct the 5 races and take all of the fastest horses in those races and have a race with them, giving you the fastest horse. Then you take the remaining 24 horses (excluding the fastest) and remove the 4th and 5th horses in the first set of 5 races (since they definitely have 3 horses faster than them), leaving you with 14 horses. Next you can remove all of the horses that were beat in the preliminary race by the horses that got 4th and 5th in the championship race, leaving you with 8 horses. Finally, you can remove the horses that remain that lost to the 3rd place horse in the final race in the preliminary race and the horse that got 3rd in the preliminary to the horse that got 2nd in the championship race, leaving you with 5 horses.
You can then run a final race where the 1st and 2nd place horses are the 2nd and 3rd fastest. Then you know the 3 fastest horses.
Riddle: A man leaves a $100,000 dollar bill on his desk and leaves work. When he returns the money is gone. He has three suspects: the cook, the cleaning lady, and the mail guy. The cook says he put the money under a book on his desk to keep it safe. They check and it is no longer there. The maid says she moved it when she was cleaning to the inside of the book between page 1 and 2. They open the book and look between page number 1 and 2 but it isn't there. The mail guy says he saw it sticking out of the book and to keep it safe he moved it to between page number 2 and 3. Once they are done the culprit is promptly arrested.
Who did it and how did he know?
Answer: The mail guy did it because if he checked between page numbers 1 and 2 page numbers 2 and 3 are opposite sides of one page and could not hold the dollar bill.