Let's look at a different example so you'll learn how:
C(12,5)
The 12 is the number you start the numerator with.
The 5 is the number you start the denominator with.
The 5 also tells you how many factors you need in the numerator,
as well as in the denominator. (You always have the same number
of factors in the numerator and denominator):
The numerator begins with 12 and has 5 factors, each one is
one less than the one before it, like this:
12×11×10×9×8
The denominator begins with 5 and also has 5 factors, each one is
one less than the one before it, like this:
5×4×3×2×1
So C(12,5) = 
Cancel the 12 in the top with the 4×3 in the bottom, like this:
C(12,5) = 
You can also cancel the 10 in the top with the 5×2 in the bottom
C(12,5) = 
so the answer is
C(12,5) = 11×9×8 = 792
You can always cancel the denominator entirely into the numerator.
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Edwin
