Data Sufficiency

Two water tanks, X and Y, were drained simultaneoulsy. 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 become empty?

1) For every 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 hr.


Answer : C

Rate at which tank drains = Amount of water drained / time taken

1) Volume of 2 tanks are 'Y' and 'Y+30' and rates are Ry (=2Rx) and Rx repectively.
Cant solve using this (2 unknows)

2) Given Rate of Ry , (alone we dont know Rx)

Together; We know Ry = Rx/2 = 20.

Hence we can solve for time Hence C

If interested in answer;

Y/20 = Y+30/40(Tank X)
Y = 30

Time = 1.5hrs

Cheese12 wrote:Two water tanks, X and Y, were drained simultaneoulsy. 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 become empty?

1) For every 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 hr.


Answer : C

Cheese12 wrote:Two water tanks, X and Y, were drained simultaneoulsy. 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 become empty?

1) For every 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 hr.


Answer : C

Rate = Q/t, Given info's Quantities relationships and time

since time equal, (Y+30)/Rx = Y/Ry .. So in order to solve we need rate ratios or quantity in any one tank..

(2) rate ratio or quantity missin.. Insufficient
(1) we have rate ratio, hence can solve for y .. but still we dont know the exact value for rate.. so insufficient

combining we get the soluion