(1) We see that tank X is drained 2 times faster than tank Y, so in order to end draining at the same time, X must contain double the water than Y.
X - Y = 30; X = 2Y => X = 60, Y = 30.
But we still don't know the drain rate yet, so we still can not calculate the time.
(2) alone is not sufficient, but it gave us the required rate. So the answer is C.
X - Y = 30; X = 2Y => X = 60, Y = 30.
But we still don't know the drain rate yet, so we still can not calculate the time.
(2) alone is not sufficient, but it gave us the required rate. So the answer is C.
