Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 7:00 am and Pipe B at 8:00 am, at what time will the pool be full?
Choose the correct choice from the following answers:
A) 16:00	B) 18:00	C) 19:00	D) 20:00	E) 17:00
Pipe A fills the pool in 4 hrs.   1 hour's work : 1/4   Pipe B empties the pool in 6 hrs.   1 hour's work : 1/6   Together if they work, 1 hour's work = 1/4 -1/6 = 1/12   Given : Pipe A started at 7:00 a.m and Pipe B at 8:00 a.m   Pool filled after 1 hour by Pipe A : 1/4 or 3/12   After 8:00 a.m   Pool filled after 1 hour with both the pipes on : 1/12   Pool filled after 9 hours with both pipes on : 9/12   Pool filled in 1 hour + Pool filled in 9 hours = 3/12 +9/12= 
<gadget id="calculator">3/12 +9/12</gadget>
<output>1</output>
1   Therefore, it takes 10 hrs to fill the pool   As Pipe A started at 7:00 a.m, pool is full at 17:00 hrs   Answer : 17:00
<result>E</result>
Pipe A fills a swimming pool in 4 hours. Pipe B empties the pool in 6 hours. If pipe A was opened at 7:00 am and Pipe B at 8:00 am, at what time will the pool be full?