# Math Help - Combinations

1. ## Combinations

Hi there,

It's been a while since I've done questions like this and my mind has gone blank. I'm completely stumped about how I would start off a question like this. I vaguely remember that theres some formula and something to do with factorials that helps solve this but not too sure.

"How many different possible combinations of 5 yellow balls and 6 red balls
can be selected from a box of 7 yellow balls and 8 red balls?

If anyone can point me in the right direction that would be great, I think I just need a slight refresher.

Many thanks,
If in doubt, rem

2. Originally Posted by monkeyhead
"How many different possible combinations of 5 yellow balls and 6 red balls can be selected from a box of 7 yellow balls and 8 red balls?
Unless we assume that the balls are all different the question is meaningless.
If the balls are different the answer is $\binom{7}{5}\binom{8}{6}$

Where $\binom{n}{k}=\frac{n!}{k!(n-k)!}$