Question

Find n so that C(n, 3) = P(n, 2).

Answer 1

n = 19/6

Explanation:

Formula for C(n,r) = n!/(r!(n-r)!)

C(n,3) = n! /( 3! * (n - 3)!)

Formula for P(n,r) = n!/(n-r)!

P(n,2)= n!/(n-2)!

C(n, 3) = P(n, 2)

n! /( 3! * (n - 3)!) = n!/(n-2)!

`(n!)/(3!(n-3)!)= (n!)/((n-2)!)` cross multiply

n!(n-2)! = n! 3! (n-3)!

(n-3)! = (n-3)(n-2)!

so n!(n-2)! = n! 3! (n-3)! becomes

n!(n-2)! = n! 3! (n-3)(n-2)! divide both sides by n!(n-2)!

1 =6(n-3)

1 =6n -18

19 = 6n

n = 19/6