There is a water tank with a capacity of 1200 litres and 10 pipes are attached to it. Some of these pipes fill the tank while others empty the tank. Each pipe can fill or empty the tank at the rate of 10 litres per minute. When all pipes are opened, a half filled tank gets completely filled in 30 minutes. How many pipes are there those empty the tank?
Solution
Correct Answer: Option C
Out of 10 pipes, let us suppose that T pipes empty the tank.
⇒ (10 - T) pipes fill the tank
Rate of filling or emptying by a pipe = 10 liters per minute
Capacity of tank = 1200 liters
Half filled tank gets completely filled in 30 minutes.
⇒ Water filled by (10 – T) pipes in 30 minutes - Water emptied by (10 – T) pipes in 30 minutes = 1200/2
⇒ (10 - T) × 10 × 30 – T × 10 × 30 = 600
⇒ (10 – 2T) × 300 = 600
⇒ 10 – 2T = 2
⇒ 2T = 8
⇒ T = 4
∴ 4 pipes are there those empty the tank.
Practice More Questions on Our App!
Download our app for free and access thousands of MCQ questions with detailed solutions