Pipes A and B can fill a tank with water in 30 minutes and 40 minutes, respectively, while pipe C can drain off 51 litres of water per minute. If all the three pipes are opened together, the tank is filled in 90 minutes. What is the capacity (in litres) of the tank?

Given:

Pipes A can fill a tank with water in 30 minutes

Pipes B can fill a tank with water in 40 minutes

Pipe C can drain off 51 litres of water per minute

All the three pipes are opened together, the tank is filled in 90 minutes

Concept used:

LCM method used,

Calculation:

According to the question:

Lcm of (30, 40, 90) = 360

Efficiency of C = (12 + 9) - 4 = 17 l/min

Which is actually 51 litres/min,

⇒ 17 unit = 51lit

⇒ 360 unit = (51/17) × 360 = 1080 litres

∴ The capacity (in litres) of the tank is 1080 litres.