There are two inlets and one outlet to a cistern. One of the inlets takes 5/2hours to fill up the cistern and the other inlet takes twice as much time to fill up the same cistern. Both of the inlets are turned on at 9:00 AM with the cistern completely empty, and at 10:30AM, the outlet is turned on and it takes 1 more hour to fill the cistern completely. How much time does the outlet working alone takes to empty the cistern when the cistern is full?	Choose the correct choice from the following choices.
A) 2 hours
B) 2.5 hours
C) 3 hours
D) 3.5 hours
E) 4 hours
The combined inflow rate of the two inlets is 2/5 + 1/5 = 3/5 cistern/hour. Thus, working together, it takes 5/3 hours (time is reciprocal of rate) to fill the cistern.   From 9:00 AM to 10:30 AM, so in 1.5=3/2 hours, the inlet pipes will fill (time)*(rate) = 3/2*3/5 = 9/10 th of the cistern .   Then the outlet is turned on and the remaining 1/10 th of the cistern is filled in 1 hour.   Letting x to be the rate of the outlet, we would have: 3/5 - x = 1/10 --&gt; x = 1/2 cistern/hour, which means that it takes 2 hours the outlet working alone to empty the cistern.   2 hoursnswer: 2 hours.
<result>A</result>
There are two inlets and one outlet to a cistern. One of the inlets takes 5/2hours to fill up the cistern and the other inlet takes twice as much time to fill up the same cistern. Both of the inlets are turned on at 9:00 AM with the cistern completely empty, and at 10:30AM, the outlet is turned on and it takes 1 more hour to fill the cistern completely. How much time does the outlet working alone takes to empty the cistern when the cistern is full?