Pipe P can drain the liquid from a tank in 3/4 the time that it takes pipe Q to drain it and in 3/3 the time that it takes pipe R to do it. If all 3 pipes operating simultaneously but independently are used to drain liquid from the tank, then pipe Q drains what portion of the liquid from the tank? Choose one.
A) 9/29  B) 8/23  C) 3/8  D) 3/11  E) 3/4
Suppose Q can drain in 1 hr. So, rQ = 1/1= 
<gadget id="calculator">1/1</gadget>
<output>1</output>
1   So, rP= 1/[(3/4)rQ] = 4/3   Also, rP = rR/(3/3) =&gt; 4/3 = rR/(3/3) =&gt; rR = 4/3   Let H is the time it takes to drain by running all 3 pipes simultaneously   So combined rate = rC = 1/H = 1 + 4/3 + 4/3 = 11/3= 1/(3/11)   Thus running simultaneously, Pipe Q will drain 3/11 of the liquid.   Thus answer = 3/11.
<result>D</result>
Pipe P can drain the liquid from a tank in 3/4 the time that it takes pipe Q to drain it and in 3/3 the time that it takes pipe R to do it. If all 3 pipes operating simultaneously but independently are used to drain liquid from the tank, then pipe Q drains what portion of the liquid from the tank?