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 20 minutes. If A, B & C are kept open successively for 1.5 minute each, how soon will the tank be filled?	Answers.
A) 2 hours B) 4 hours C) 5 hours D) 2 hours 15 min E) 3 hours
in three minute 1/20+1/30-1/20=2/60 = 1/30 part is filled   4.5 min--------1/30 parts   x min--------- 1 part(full)   x=135 min =2 hours 15 min   ANSWER:2 hours 15 min
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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 20 minutes. If A, B & C are kept open successively for 1.5 minute each, how soon will the tank be filled?