GMAT Quantitative Reasoning Practice Test 1

Question : 87 of 100

Marks: +1, -0

Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 8:00 am and Pipe B at 9:00 am, at what time will the pool be full?

$15: 00$
$17: 00$
$18: 00$
$19: 00$
20:00

Validate

Solution:

From 8:00 am to 9:00 am, Pipe A, which fills the pool in 4 hours, was open for one hour, filling one quarter of the pool. From 9:00 am, the two Pipes worked together at the rate of:

1 / 4-1 / 6=1 / 12

, one pool in 12 hours. Since the pool was already one quarter full at 9: 00 am, it will take only 9 hours to fill the remaining three quarters of the pool. 9 hours from 9: 00 am is 18: 00.

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