two puzzles for the price of zero:
using four '9's and addition, subtraction, multiplication, and division, find and expression that evaluates to 100.
(everything is in base 10)
there are 100 prisoners standing in a line, facing front. Each prisoner has either a white or a black hat on. Since they are in the line, each prisoner can see the hat of every man in front of him (the person at the back can see 99 hats). Starting from the back of the line, and going to the front, each is asked what color hat they have. If they are right, they live, wrong, they die. How many prisoners can be saved, and how should they do it?