Question

If ⁿP_r = 1680 and ⁿC_r = 70, find n and r.

Answer 1

Given that ⁿP_r = 1680, ⁿC_r = 70 

We know that ⁿC_r = \(\frac{nP_r}{r!}\)

70 = \(\frac{1680}{r!}\)

r! = \(\frac{1680}{70}\) = 24 

r! = 4 x 3 x 2 x 1 = 4! 

∴ r = 4