Question

If ${}^n{P}_r=720$ and ${}^n{C}_r=120$, then what is the value of 'r'.

Answer 1

${}^n{P}_r=720$ & ${}^n{C}_r=120$

As ${}^n{P}_r=r{!}^n{C}_r\Rightarrow r!=6$

$r=3$