Question

Which expression represents the number of possible combinations of n items taken rat a time?

n!
(n-nin
n!
(n-
(n-1)!
n!
(n-1)!!
n!

Answer 1

nCr = n! / (r!)(n-r!).

Explanation:

That would be nCr = n! / (r!)(n-r!). A quick way of working these out is as follows: Take 7C4: this is 7*6*5*4/4*3*2*1 Cancelling out the 4 and 3*2: = 7*5 = 35 15C12 = 15C(15-12) = 15C3 = 15*14*13 / 3*2*1 = 5*7*13 = 455.