Bunuel wrote:
Two water tanks, X and Y, were drained simultaneously. If X contained 30 more gallons of water than Y, and both tanks became empty at the same time, how long did it take the tanks to empty?
(1) For ever gallon drained from tank Y, 2 gallons were drained from tank X.
(2) Tank Y was drained at a constant rate of 20 gallons per hour.
Since both the tanks empty at the same time, to find the time to empty the tanks, we need to know the volume of water in the any of the two tanks and rate of drainage from any of the two tanks.
(1) Let the volume of water in tank X and Y be x and y gallons.
Combining this statement and x=y+30, we get x=60 and y=30.
However, we don't know the rate of drainage from any of the tanks, so we can't find time to empty the tanks.
Thus, insufficient.
(2) This statement doesn't give any information on the volume of water in tank Y, so we can't find time taken to empty tank Y.
Thus, insufficient.
From (1) and (2) together, we get that y=30 and that tank Y was drained at a constant rate of 20 gallons/hour.
=> Time taken to drain tank Y= 30/20= 1.5 hours.
Thus, sufficient.
Therefore, the answer is option C.
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