A tank is filled in 5 hours by three pipes P, Q and R. The pipe R is twice as fast as Q and Q is twice as fast as P. How much time will pipe P alone take to fill the tank?  Options
A) 35 hrs B) 20 hrs C) 25 hrs D) 50 hrs E) 28 hrs
Pipe P alone - x hrs to fill   then Q and R -&gt; x/2 and x/4 hrs   then 1/x+2/x+4/x = 1/5   7/x=1/5   x = 33 hrs   35 hrsNSWER 35 hrs
<result>A</result>
A tank is filled in 5 hours by three pipes P, Q and R. The pipe R is twice as fast as Q and Q is twice as fast as P. How much time will pipe P alone take to fill the tank?