Two taps can separately fill a cistern 4 minutes and 6 minutes respectively and when the waste pipe is open, they can together fill it in 8 minutes. The waste pipe can empty the full cistern in?
Choose one
A) 7
B) 8
C) 6
D) 9
E) 3.4
1/4 + 1/6 - 1/x = 1/8   x = 24/7 = 3.4   Answer: 3.4
<result>E</result>
Two taps can separately fill a cistern 4 minutes and 6 minutes respectively and when the waste pipe is open, they can together fill it in 8 minutes. The waste pipe can empty the full cistern in?