6.Permutation and Combination
hard

$r$ ની .  .  . . કિમંત માટે $^{20}{C_r}^{20}{C_0}{ + ^{20}}{C_{r - 1}}^{20}{C_1}{ + ^{20}}{C_{r - 2}}^{20}{C_2} + ...{ + ^{20}}{C_0}^{20}{C_r}$ ની કિમંત મહતમ મળે.

A

$15$

B

$20$

C

$11$

D

$10$

(JEE MAIN-2019)

Solution

$^{20}{C_r}{.^{20}}{C_0}{ + ^{20}}{C_{r – 1}}{.^{20}}{C_1} + ……{ + ^{20}}{C_0}{.^{20}}{C_r} = $

Selecting $r$ student from $20$ boys and $20$ girls ${ = ^{40}}{C_r}$

$^{40}{C_r}$ will be maximum if $r=20.$

Standard 11
Mathematics

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