Boiling An Egg
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 can you boil the egg for only two minutes?
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?