Question

The mean of coefficients of x, x2, ....., x7 in the binomial expansion of (2 + x)9 is?

Answer 1

Sum of coefficients = $^9C_1.2^8+^9C_2.2^7.....+^9C_7.2^2$
$\Rightarrow 3^9-2^9-19=19683-572-19 = 19152$
Mean = $\frac{sum}{7}=\frac{19152}{7}=2736$
$\therefore$ the correct answer is $2736$.