rsanchez wrote:

gsr, how did u determine the frequencies? could u please explain your logic? I'm having a hard time grasping the info in the question.

The frequencies are in Geometric progression (each successive one is over the other by a constant ratio 'r') -

If f is the 1st freq, then 2nd freq is f*r

Third freq is (f*r)*r = f*r^2

Fourh freq is (f*r^2)*r = f*r^3

13th = f*r^12

We are given two things

1. First frequency = f = 440

2. 13th freq = 2*(1st freq) => f = 2*f^12

Asked is 7th freq = f*r^6

Since the answers are in terms of sqrt(2), taking square root on both sides,

r^6 = sqrt(2)

So, f*r^6 = 440*sqrt(2) [choice A]

Hope this is clear