A cistern can be filled by 3 pipes in 30, 40 and 60 min and emptied by an escape pipe in half an hour the 3 taps are turned on at noon but the escape pipe is at the same time accidentally left open and not closed for a quarter of an hour at what time will the cistern be full?
Choose the correct answer:  A) 60 min  B) 90 min  C) 120 min  D) 150 min  E) 170 min
Explanation:   Let the total time be x min   x/30 + x/40 + x/60 – x/15 = 1   =&gt; x = 120 min   Answer: Option 120 min
<result>C</result>
A cistern can be filled by 3 pipes in 30, 40 and 60 min and emptied by an escape pipe in half an hour the 3 taps are turned on at noon but the escape pipe is at the same time accidentally left open and not closed for a quarter of an hour at what time will the cistern be full?