Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 4 minutes A is turned off. After how much more time will the cistern be filled? Options.
A) 6	B) 8 1/1	C) 8 1/4	D) 8 1/2	E) 8 3/7
4/12 + (4 + x)/15 = 1   x = 6   6nswer: 6
<result>A</result>
Two pipes A and B can fill a cistern in 12 and 15 minutes respectively. Both are opened together but after 4 minutes A is turned off. After how much more time will the cistern be filled?