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Questions  

 Series nC1+1nC2+2nC3++nnCn is equal to

a
n2n−1
b
2n−1
c
n2n
d
23−1

detailed solution

Correct option is A

Since, (1+x)n=nC0+nC1x+nCx2+…+nCnxn  Ondifferentiatingw.r.t., x, weget n(1+x)n−1=0+nC1+2⋅x⋅nC2+…+n⋅nCnxn−1Put x=1, we get n(1+1)n−1=nC1+2⋅nC2+…+n⋅nCn⇒  n2n−1=nC1+2⋅nC2+…+n⋅nCn

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