If ^n{Cᵣ} = {,^n}{C_{r - 1}} and ^n{Pᵣ}{ = ^n}{P_{r + 1}} , then value of n is

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Gujarati

Hindi

6.Permutation and Combination

medium

If $^n{C_r} = {\,^n}{C_{r - 1}}$ and $^n{P_r}{ = ^n}{P_{r + 1}}$, then the value of $n$ is

A

$3$

B

$4$

C

$2$

D

$5$

Solution

(a) The conditions provided that $n – r = r – 1$ ==> $r = \frac{{n + 1}}{2}$.

So if we put $n = 3$, then $r = 2$ satisfies the conditions.

Standard 11

Mathematics

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