Q50 / 90 · JEE Main 2021 (25 Jul Shift 2) · Mathematics

Let n∈N and x denote the greatest integer less than or equal to x. If the sum of n+1 terms of C0n,3·C1n,5·C2n,7·C3n,… is equal to 2100·101, then 2n-12 is equal to

Correct answer: 98

Solution

Let S=C0n+3C1n+5.C2n+…+2n+1·Cnn

Now, Tr=2r+1nCr

Therefore, S=ΣTr

S=Σ2r+1nCr

=Σ2rnCr+ΣnCr

⇒S=2n·2n-1+2n=2nn+1

⇒2nn+1=2100.101

⇒n=100

Now, 2n-12=2992=98.

Hence, the correct answer is 98.

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