Question

Find n, if $\rm ^{n}C_{n-4} =15$

Answer 1

Answer:

n = 6

Step-by-step explanation:

Hi,

We Know that nCr = n!/(n-r)!4!

so ⁿCn₋4 = n!/4!(n-4)!

Given ⁿCn₋4 = 15

Thus,  n!/4!(n-4)! = 15

n(n-1)(n-2)(n-3) = 24*15

n(n-1)(n-2)(n-3) = 6*5*4*3

We can observe that n = 6 satisfy the above equation

Hence, the value of n is 6

Hope, it helps !