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  4. For 2 ge r le n, nCr +2⋅ nCr- 1 + nCr-2 is equal to

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Q. For $ 2 \ge r \le n, ^nC_r +2\cdot ^nC_{r- 1} + ^nC_{r-2} $ is equal to

AMUAMU 2010Permutations and Combinations

Solution:

Correct answer is (d) $ ^{n+2}C_{r} $