Brain Teasers

1. Con-Fusing Puzzle: In front of you are several long fuses. You know they burn for exactly one hour after you light them at one end. The entire fuse does not necessarily burn at a constant speed. For example, it might take five minutes to burn through half the fuse and fifty-five minutes to burn the other half.
With a match-box and using these fuses, how can you measure exactly three-quarters of an hour of time?

2. Egg Puzzle: You need to boil eggs for exactly 9 minutes, or else your nitpicky guest will complain, and you will lose your job as head chef.
But you have only 2 hourglasses; one measures 7-minutes, and the other measures 4-minutes. How can you correctly measure 9 minutes?

3. Matchstick Puzzle: There are five squares (one 3x3 and four 1x1) formed with 20 matchsticks, as shown in the illustration. Move two matchstick to get seven squares. Overlapping or breaking of matchsticks or "loose ends" are not allowed.

Adapted from: http://www.mathsisfun.com/