A pool can be filled in 4 hours and drained in 5 hours. The valve that fills the pool was opened at 9:00 am and some time later the drain that empties the pool was also opened. If the pool was filled by 6:00 pm and not earlier, when was the drain opened?
Options:	A) 10:45 am	B) 11:45 am	C) 12:45 pm	D) 1:45 pm	E) 2:45 pm
The filling rate is 1/4 and the draining rate is 1/5.   The combined rate of filling and draining is 1/4 - 1/5 = 1/20.   Let x be the number of hours before the drain was opened.   x/4 + (9-x)/20 = 1   5x + 9 - x = 20   4x = 11   x = 2.75   The answer is 11:45 am.   The answer is 11:45 am.
<result>B</result>
A pool can be filled in 4 hours and drained in 5 hours. The valve that fills the pool was opened at 9:00 am and some time later the drain that empties the pool was also opened. If the pool was filled by 6:00 pm and not earlier, when was the drain opened?