Indicate the formula for the following conditions.C(n,r)

The formula for C(n,r), also known as "n choose r" or a combination,
is: 
nCr = n! / (r!(n-r)!),
where n is the total number of options and r is number you must choose

The number generated is the total number of possible combinations. 

The ! means factorial. For example, 4! = 4 x 3 x 2 x 1