Pipe A that can fill a tank in an hour and pipe B that can fill the tank in half an hour are opened simultaneously when the tank is empty. Pipe B is shut 10 minutes before the tank overflows. When will the tank overflow? Choose the correct answer:
A) 37 mins  B) 35 mins  C) 40 mins  D) 32 mins  E) 36 mins
The last 10 minutes only pipe A was open. Since it needs 1 hour to fill the tank, then in 10 minutes it fills 1/5th of the tank, thus 5/6 of the tank is filled with both pipes open.   The combined rate of two pipes is  1 + 2= 
<gadget id="calculator"> 1 + 2</gadget>
<output>3</output>
3 tanks/hour, therefore to fill 5/6th of the tank they need (time)= (work)/(rate) = (5/6)/3 = 5/18 hours = 27 minutes.   Total time = 10+ 27= 
<gadget id="calculator">10+ 27</gadget>
<output>37</output>
37 minutes.   37 minsnswer: 37 mins.
<result>A</result>
Pipe A that can fill a tank in an hour and pipe B that can fill the tank in half an hour are opened simultaneously when the tank is empty. Pipe B is shut 10 minutes before the tank overflows. When will the tank overflow?