Two water tanks, X and Y, were drained simultaneously. If X contained

Time = Work/Rate

Given : Time for X = Time for Y

= Wx/Rx = Wy/Ry
= Wy+30/Rx=Wy/Ry

From (1) we will get the value of Wy but not the rate. Not sufficient.

From (2) we will get the value of Ry but not Wy. Not sufficient.

Together (1) & (2), sufficient.

Answer :C

Hello Bunuel
I have a doubt.
why cannot the answer be E
Because the time spends on the number of gallons present in the tanks right?
So, Atleast we need to know any one of the x or y.But we don't know anyone of them and the time changes based on the number of gallons right?
please explain .Thankyou.

I will try to explain that we don't need capacity of X & Y
from 1 & 2 r1(rate for x) = 40 bcoz r2(rate for y)=20
40 * t = 30+y
20 *t =y

2 equations . We can find y & t

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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