Question

Consider two GPs $2,2^2, 2^3, \ldots$ and $4,4^2$, $4^3, \ldots$ of 60 and $n$ terms respectively. If the geometric mean of all the $60+ n$ terms is $(2)^{\frac{225}{8}}$, then $\displaystyle\sum_{ k =1}^{ n } k ( n - k )$ is equal to :

• A. 560
• B. 1540
• C. 1330
• D. 2600

Answer 1

Answer: (C)

1330

Answer 2

The correct option is (C): 1330