luminousmocha wrote:

#33

Working at a constant rate respectively, pumps X and Y took 48 hours to fill an empty water tank. What fraction of the water in a full tank came from pump X?

(1) working alone at its constant rate, pump X would have taken 80 minutes to fill tank with water

(2) working alone at its constant rate, pump y would have taken 120 minutes to fill up the tank

Answer: (D)

I am not too sure how this answer is derived. Is it from finding out what fraction of the individual rate is over the rate of X+Y?

I hope its 48mins in the question stem

given x and y together take 48mins.

this is derived as 1/X + 1/Y = 1/48 [work-time concept]

stmnt1 - Pump X takes 80mins to fill the tank. here either we can find out the time taken by Y and then doing the calculations to find the ratio.

else since X takes 80mins to fill the tank so in 48mins it will fill 48/80 * 100 = 60% of the tank. hence suff

stmnt2 - we have Y = 120. either we calculate value of X and then find the ratio or similarly since Y takes 120mins

to fill tank then in 48mins it will fill 48/120 * 100 = 40%. the remaining 60% is filled by X. hence suff

so D