Working alone at its constant rate, pump A pumped out ¼ of the water in a tank in 2 hours. Then pumps B and C started working and the three pumps, working simultaneously at their respective constant rates, pumped out the rest of the water in 3 hours. If pump B, working alone at its constant rate, would have taken 18 hours to pump out the rest of the water, how many hours would it have taken pump C, working alone at its constant rate, to pump out all of the water that was pumped out of the tank?  Answers
A) 6  B) 12  C) 15  D) 18  E) 24
Rate of pump A = 1/8   3 hours are required to pump out the remaining (3/4)ths of tank --&gt; 1 hr to pump out 1/4   Rate of A + Rate of B + Rate of C = 1/4   Rate of B + Rate of C = 1/4 - 1/8 = 1/8   B takes 18 hours to pump out the remaining (3/4)ths of tank --&gt; 6 hrs per (1/4)ths --&gt; 24 hrs to pump out fully.   Rate of 12 = 1/24   1/24 + Rate of C = 1/8   Rate of C = 1/8 - 1/24 = 1/12   Time required to pump out all the water by C = 12 hrs   Answer: 12
<result>B</result>
Working alone at its constant rate, pump A pumped out ¼ of the water in a tank in 2 hours. Then pumps B and C started working and the three pumps, working simultaneously at their respective constant rates, pumped out the rest of the water in 3 hours. If pump B, working alone at its constant rate, would have taken 18 hours to pump out the rest of the water, how many hours would it have taken pump C, working alone at its constant rate, to pump out all of the water that was pumped out of the tank?