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The coefficient of the 5th term in the binomial expansion of...

The coefficient of the 5th term in the binomial expansion of (1+kx)8, in ascending powers of x is 358. Find the value of the constant k.

A.

2

B.

12

C.

12

D.

-2

Correct answer is B

(1+kx)8=8C0(18)(kx)0+8C1(17)(kx)1+...

The 5th term = 8C51(14)(kx)4

= 8C4(kx)4

70k4=358

k4=35870

k4=116

k=12