Horse racing and three other puzzles (*)
Horse racing You have 25 horses, and you want to find out which 3 are the fastest. You don't have a stop watch, but you do have a race track that you can fit 5 horses on. What is the minimum number of races you need to run to identify the fastest three horses, and what are those races?
A whole lot of money You are blindfolded. On the table in front of you are a number of ordinary coins. You are told that exactly 26 coins show heads. Your challenge (while blindfolded): Divide the coins into two sets so that the same number of coins in each set show heads. (There is no way for you to tell, by sight or touch, which coins are showing heads or tails.)
Mirror mirror Why do mirrors reverse left and right, but not up and down?
Burning ropes You have two ropes of different materials and length. However, both ropes take exactly 60 minutes to burn out completely from one end to the other. Without cutting them, how do you burn these ropes to measure exactly 45 minutes?