If $^n{P_r}$=$ 720$.$^n{C_r},$ then $r$ is equal to
$6$
$5$
$4$
$7$
(a) $^n{P_r}\, = 720.{\,^n}{C_r}$
==> $^n{P_r}\, \div {\,^n}{C_r}\, = 720$
==> $\,r\,! = 720 = 6\,!$
$==> r = 6.$
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