If ^n P_r = 720.^n C_r , then r is equal to - Vidyadip

Question

If $^n{P_r}$=$ 720$.$^n{C_r},$ then $r$ is equal to

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Answer

a
(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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