Question

n!
r!(n-r)!
(n-r)!
n!
r! = 1320 - 6)
220
*3*2*1
r = 3
= 3 * 2x
=
= 30
3
!​

Answer 1

nCr=nPr/r!

nCr*r!=nPr

220*r!=1320

r!=6

r=3

nP3=n!/(n-3)!=1320

n*(n-1)*(n-2)=1320

n^3-3n^2+2n=1320

n^3-3n^2+2n-1320=0

n=12

.

Ed