If ^nC_ n-r +3 ^nC_ n-r+1 +3 ^nC_ n-r+2 + ^nC_ n-r+3 = ^xC_r, then x=

JEE Main Mathematics question

If {}^nC_{n-r}+3\cdot{}^nC_{n-r+1}+3\cdot{}^nC_{n-r+2}+{}^nC_{n-r+3}={}^xC_r, then

Answer: (C)

Use : the terms become {}^nC_r+3\cdot{}^nC_{r-1}+3\cdot{}^nC_{r-2}+{}^nC_{r-3}. The coefficients

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Question ID VK-020758