Two taps can separately fill a cistern 10 minutes and 15 minutes respectively and when the waste pipe is open, they can together fill it in 36 minutes. The waste pipe can empty the full cistern in?  Select the correct option
A) 8.2
B) 7.2
C) 6.2
D) 9.2
E) 5.2
1/10 + 1/15 - 1/x = 1/36   x = 7.2   Answer:7.2
<result>B</result>
Two taps can separately fill a cistern 10 minutes and 15 minutes respectively and when the waste pipe is open, they can together fill it in 36 minutes. The waste pipe can empty the full cistern in?