- #1
the4thamigo_uk
- 47
- 0
Homework Statement
If (N,R) indicates number of combinations of R objects selected from set of N objects N >=r then prove :
R
E (N,r) x (M,R-r) = (N+M, R)
r=0
E specifies the usual capital sigma notion for a sum.
The Attempt at a Solution
Just don't know how to tackle this? Inductive proof may be possible but we have three variables N, M and R, so its non trivial?
Any clues?