Two pipes A and B can fill a cistern in 22 and 44 minutes respectively, and a third pipe C can empty it in 48 minutes. How long will it take to fill the cistern if all the three are opened at the same time? Choose one
A) 18 1/9 min	B) 21 1/8 min	C) 21 3/25 min	D) 18 8/7 min	E) 19 3/7 min
1/22 + 1/44 - 1/48   =25/528   528/25 = 21 3/25   Answer:21 3/25 min
<result>C</result>
Two pipes A and B can fill a cistern in 22 and 44 minutes respectively, and a third pipe C can empty it in 48 minutes. How long will it take to fill the cistern if all the three are opened at the same time?