Permutation questions- urgent help needed

DrSteve
Wed, 23 Jan 2013 13:46:05 +0000

Here’s a challenging counting problem if you’d really like to sharpen your permutation/combination skills. Note that this is much harder than any problem that will ever appear on an SAT:

Let j and k be positive integers with j≤k. In how many ways can k be written as a sum of j positive integers?

Hint: The answer can be written as either aPb or aCb for some a and b.