Question

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

Answer 1

B

Explanation:

Answer 2

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.