Can anyone help me prove this factorial, or give me an idea as to why this might be true...
(n¦x) *(m¦t-x) = (n+m¦t)
That is, n choose x times m choose (t-x) is equal to n+m choose t.
Thanks in advance!
With the sum it is Chu-Vandermonde identity:
Vandermonde's identity - Wikipedia, the free encyclopedia
Chu-Vandermonde Identity - ProofWiki