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Question

Question: For 3 £ r £ n <sup>n</sup>C<sub>r</sub> + 3 <sup>n</sup>C<sub>r–1</sub>+ 3 <sup>n</sup>C<sub>r–2 +</...

For 3 £ r £ n nCr + 3 nCr–1+ 3 nCr–2 + nCr–3 is-

A

n+3Cr

B

2 n+2Cr+2

C

3 n+1Cr+1

D

3 nCr

Answer

n+3Cr

Explanation

Solution

Use nCr + nCr–1 = n+1Cr

nCr + nCr–1 + 2(nCr–1 + nCr–2) + nCr–2 + nCr–3