The coefficient of t^(2) in the expansio...

The coefficient of `t^(2)` in the expansion of `1 cdot (1+t)^(20)+ 2t (1+t)^(19)+3t^(2)(1+t)^(18)+….+20t^(20) (1+t)+21t^(21)` is

A

a) 141

B

b) 231

C

c) 272

D

d) 371

Verified by Experts

The correct Answer is:

B

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