If $^nPr = 720$ and $^nCr = 120$, find the value of $r$.

Question

Accepted Answer

We know the relation between permutation and combination: $^nPr = ^nCr 	imes r!$. Substituting the given values, $720 = 120 	imes r! \implies r! = \frac{720}{120} = 6$. Since $3! = 6$, we get $r = 3$. Therefore, option B is correct.

Permutations and Combinations

❓ Sibling Questions in this Chapter