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Questions  

 If Sn=i=0n1 nCr and tn=r=0nr nCr then tnSn=

a
12n
b
2n−12
c
n−1
d
12n−1

detailed solution

Correct option is A

tn=∑r=0n r nCr=∑r=0n n−r nCn−r=∑r=0n n−r nCr=n∑r=0n 1 nCr−∑r=0n r nCr=nsn−tn⇒2tn=nsn⇒tnSn=n2

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