Three pipes, A, B, & C are attached to a tank. A & B can fill it in 20 & 30 minutes respectively while C can empty it in 15 minutes. If A, B & C are kept open successively for 2 minute each, how soon will the tank be filled? Choose the correct choice from the following options: A) 2 hours B) 4 hours C) 3 hours D) 5 hours E) 6 hours
in three minute 1/20+1/30-1/15=1/60 part is filled   6 min--------1/60 parts   x min--------- 1 part(full)   x=360 min =6 hours   ANSW6 hoursR:6 hours
<result>E</result>
Three pipes, A, B, & C are attached to a tank. A & B can fill it in 20 & 30 minutes respectively while C can empty it in 15 minutes. If A, B & C are kept open successively for 2 minute each, how soon will the tank be filled?