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 4 minute each, how soon will the tank be filled?
Choose the correct choice from the following options.
A) 2 hours
B) 12 hours
C) 3 hours
D) 5 hours
E) 6 hours
in three minute 1/20+1/30-1/15=1/60 part is filled   12 min--------1/60 parts   x min--------- 1 part(full)   x=720 min =12 hours   ANSWER:12 hours
<result>B</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 4 minute each, how soon will the tank be filled?