Question

What is 1 * 2 * 3 * 4 * 5 all the way to 100?

Answer 1

The answer is 5050, it's a programming exercise I sometimes set. Mathematically though you can do this in your head far faster than you can write a program to do it. How many of these sums are there? Clearly there are 100/2 = 50 sums.