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The value of r for which .^(20)C(r)xx.^(...

The value of r for which `.^(20)C_(r)xx.^(20)C_(0)+.^(20)C_(r-1)xx.^(20)C_(1)+.^(20)C_(r-2)xx.^(20)C_(2)+...+.^(20)C_(0)xx.^(20)C_(r)` is maximum is

A

15

B

11

C

10

D

20

Text Solution

Verified by Experts

The correct Answer is:
D
The given series is : `.^20C_r .^20C_0 + .^20C_(r-1) .^20C_1` + ….+ `.^20C_0 .^20C_r = .^(20+20)C_r=.^40C-r`
To maximize `.^40C_r` , r should be equal to `40/2`=20.
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