Question

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 1 minute each, how soon will the tank be filled?

Answer 1

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 1 minute each, how soon will the tank be filled?
Ans: In one minute pipe A will fill = 1/20
⟹ In two minute pipe A and B will fill = 1/20 +1/30
⟹ In three minute pipe A, B and C will fill = 1/20 +1/30 - 1/15
= 1/60
⟹ Let the number intervals of three minutes be x
x/60 +1/20 +1/30 = 1
x + 5 = 60
x = 55
⟹ Time needed to fill the tank completely is = 55?3 + 2
( after 55 intervals of 3 minutes pipe A pipe B will take 1 minute each i.e 2 minutes) = 167 minutes.

Answer 2

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