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The answer given is C and even i got E ( explanation similar to dushver's).

Alex_NL, we cant say that if m^2/n = 7/5, then m/n^2 = sqrt7/25.
We can prove this by plugging some values.
m=6,n=8.
m^2/n=36/8=9/2
m/n^2=6/64 (actual value)
m/n^2 (per your method) = 3/4.
these two are not equal.
Thanks.

1. The ratio of m^2 to 1 is 7/5
2. The ratio of m^2 to n is 7/5

From 1, nothing is said about n, so it is insufficient.

From 2, it can be written as m^2/n = 7/5, 5m^2 = 7n, n = (5m^2)/7
So using this, m/n^2 = 7m/25m^4 = 7/25m^3. Still we canâ€™t figure out what the ratio is.

Using 1 and 2, we can see that n is actually 1, so with this in hand, we can get 5m^2=7n,
5m^2=7, m = sqrt(7/5). So m:n^2 = sqrt(7/5): 1. Sufficient.