I do wish my high school combinatorics had included Stirling's approximation. It allows great approximations for problems that are really asking for it. If th

I do wish my high school combinatorics had included Stirling's approximation. It allows great approximations for problems that are really asking for it. If there are 200 white and 200 black balls in an urn, there's no sense asking for some expected value as an exact rational number.