Subject: General Aptitude · Chapter: Pipes and Cisterns · Exam: · Marks: · Difficulty:
Eight pipes are fitted to a water tank. Some of these are water pipes to fill the tank and the remaining are waste pipes used to empty the tank. Each water pipe can fill the tank in 12 hours and each waste pipe can empty it in 36 hours. On opening all the pipes an empty tank is filled in 3 hours. The number of waste pipes is
(a)2
(b)3
(c)4
(d)5
Answer
Answer (as printed): B
Explanation
Let there be x water pipes and (8 – x) waste pipes. 1 Now, part filled by each water pipe = ; part emptied 12 1 by each waste pipe = . 36 x (8 − x ) 1 ∴ − = ⇔ 3x – (8 – x) = 12 ⇔ 4x = 20 12 36 3 ⇔ x = 5. So, number of waste pipes = (8 – 5) = 3. 519 1 3 1
Explanation as extracted from the printed page; notation may be imperfect.