Two taps can separately fill a cistern 7 minutes and 14 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 the correct choice from the following:
A) 6.2
B) 8.2
C) 11.2
D) 9.2
E) 7.2
1/7 + 1/14 - 1/x = 1/8   x = 11.2   Answer:11.2
<result>C</result>
Two taps can separately fill a cistern 7 minutes and 14 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?