Given the definition of a mathematical combination:

n C r

where n is the total number of selections and r is the number you are choosing from the pool.

The formula for evaluation is:

r! (n-r)!

What is the answer when you evaluate the following expression:

17 C 10 - 30 C 12 + 50 C 3

ok I admit I struggled with this one... I guess the main thing in understanding what the question is asking... a good place for information on this is HERE. Once you have an understanding of the functions you will need, I simply googled for a combination function: HERE
(I don't see a problem using code snippets like this as long as you understand them they are simply making your job easier, and there not solving it, just helping with a generic math function). then it's just a case of knowing what to add and subtract.