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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