Question

What is the value of 10C7?

A.12
B.720
C.5040
D.604,800

Answer 1

The answer is 120

For combinations we use:
nCr = n!/(r!(n-r)!)
10C7 = ?
n = 10
r = 7

10C7 = 10!/(7!(10-7)!)
         = (10*9*8*7*6*5*4*3*2*1)/(7*6*5*4*3*2*1*3!)
         = 3628800/(5040 * 3*2*1) 
         = 3628800/30240
         = 120