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Question

Question: If <sup>n</sup>C<sub>4</sub> = 210, then <sup>12</sup>C<sub>n</sub>....

If nC4 = 210, then 12Cn.

A

33

B

22

C

11

D

66

Answer

66

Explanation

Solution

n(n1)(n2)(n3)24=210.\frac{\mathbf{n(n}\mathbf{-}\mathbf{1)(n}\mathbf{-}\mathbf{2)(n}\mathbf{-}\mathbf{3)}}{\mathbf{24}}\mathbf{= 210.}

n(n - 1) (n - 2) (n - 3) = 210 x 24 = 7 x 3 x 5 x 2 x 4 x 3 x 2

= 7 x 8 x 9 x 10.

n = 10.

12Cn = 12C10 = 12C2 = 12x112\frac{12x11}{2} = 66.