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 9 minutes. The waste pipe can empty the full cistern in?	Choose the correct choice from the following:
A) 18	B) 17	C) 16	D) 19	E) 15
1/10 + 1/15 - 1/x = 1/9   x = 18   18nswer:18
<result>A</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 9 minutes. The waste pipe can empty the full cistern in?