# Homework Help: A couple Discrete Math Questions

1. Apr 14, 2013

### Texans80mvp

For the first question it deals with onto functions I was able to do a-e which deals with actal numbers. Then questions E stumped me. I have no idea what to do or even how to start. It reads:

Let C (n,m) be the number of onto functions from a set of m elements to a set of n elements, where m > n > 1 (All of those are greater than or equal to signs). Find a formula relating C (n,m) to C (m-1,n) and C (m-1,n-1).

The second question deals with relations on a Cartesian product of A. A is a set with 8 elements. I was able to figure out that there are 2^64 relations total and 2^8 are reflexive while 2^36 are symmetric. However how many are both reflexive and symmetric? The question reads:

A is a set with eight elements.
How many relations on A are both reflexive and symmetric?

Any help would be greatly appreciated, even a point in the right direction would help. But like I said I am stuck and have almost no clue on what to do for either problem.