One pipe can fill a pool 1.25 times faster than a second...

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One pipe can fill a pool 1.25 times faster than second pipe. When two pipes are opened, they fill the pool in five hours. How long would it take to fill the pool if only the slower pipe is used?

A. 11.25
B. 11.52
C. 1.25
D. 9
E. 7.2

The OA is A.

Please, can any expert explain this PS question for me? I can't get the correct answer. I need your help. Thanks.
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by GMATGuruNY » Sat Dec 23, 2017 9:15 pm
swerve wrote:One pipe can fill a pool 1.25 times faster than second pipe. When two pipes are opened, they fill the pool in five hours. How long would it take to fill the pool if only the slower pipe is used?

A. 11.25
B. 11.52
C. 1.25
D. 9
E. 7.2
Let rate for the slower pipe = 4 liters per hour.
Since the faster pipe is 1.25 times faster, the rate for the faster pipe = (1.25)(4) = 5 liters per hour.
Combined rate for the two pipes = 4+5 = 9 liters per hour.
Since the two pipes working together at a rate of 9 liters per hour can fill the pool in 5 hours, the pool = rt = 9*5 = 45 liters.
Since the slower pipe's rate = 4 liters per hour, the time for the slower pipe to fill the 45-liter pool = w/r = 45/4 = 11.25 hours.

The correct answer is A.
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by GMATWisdom » Sun Dec 24, 2017 11:03 am
swerve wrote:One pipe can fill a pool 1.25 times faster than second pipe. When two pipes are opened, they fill the pool in five hours. How long would it take to fill the pool if only the slower pipe is used?

A. 11.25
B. 11.52
C. 1.25
D. 9
E. 7.2

The OA is A.

Please, can any expert explain this PS question for me? I can't get the correct answer. I need your help. Thanks.
ASSUMING THE SLOWER PIPE FILLS THE TANK AT Y LITERS PER HOUR THEN SPEED OF FASTER PIPE WOULD BE
1.25Y
AND THEIR TOGETHER SPEED WOULD BE Y+1.25Y = 2.25Y LITERS PER HOUR.
SINCE THEY FILL THE TANK IN 5 HOURS, THE CAPACITY OF THE TANK WOULD BE= 2.25Y*5=11.25Y
TIME TAKEN FOR A PIPE TO FILL THE TANK = CAPACITY OF THE TANK / SPEED OF FILLING

HENCE SLOWER PIPE WILL FILL THE TANK IN (11.25Y)/ Y = 11.25
HENCE OPTION A