Question

If one pipe A can fill the tank in 10 hours then 4 pipes each of efficiency 20% as that of Pipe A can fill the same tank in how many hours?

• A. 15 hrs
• B. 12 hrs
• C. 10 hrs
• D. 12.5 hrs

Answer 1

The correct option is D

12.5 hrs

Suppose in one hour A can fill 100 litres.

As it fills the tank in 10 hours, the capacity of the tank is 100 * 10 = 1000 litres.

Now 4 pipes each with efficiency 20% as that of Pipe A à

Each of the 4 pipes will fill 20 litres in 1 hour. So, all together they will fill 80 litres in one hour.

So, to fill the tank completely, they will take 1000/80 = 12.5 hours.

Using constant product rule

The 4 pipes have a efficiency = 20% that of A

Together they have an efficiency = 80% that of A.

Thus, decrease in efficiency = 1/5

Increase in time = 1/4 = 25% more than 10 hours = 12.5 hours.