A pipe can fill a cistern in 20 minutes whereas the cistern when full

1.	A pipe can fill a cistern in 20 minutes whereas the cistern when full can be emptied by a leak in 28 minutes. When both are opened, The time taken to fill the cistern is:1. 80 min2. 70 min3. 60 min4. 48 min
Answer» Correct Answer - Option 2 : 70 min Given: A pipe can fill a cistern in 20 minutes. Time taken by the leak to empty the tank = 28 minutes. Concept used: If a pipe can fill a tank in x hours then it can fill 1/x part of the tank in 1 hour. Calculation: Let the time taken by a pipe to fill the tank when the leakage arises be 1 minutes is 1/20 part. And the time taken by a pipe to empty the tank be 1 minutes is 1/28 part. When both pipes are opened, The tank fills in 1 minute = 1/20 - 1/28 ⇒ (7 - 5)/140 ⇒ 2/140 ⇒ 1/70 part ∴ The time taken to fill the tank is 70 minutes.

A pipe can fill a cistern in 20 minutes whereas the cistern when full can be emptied by a leak in 28 minutes. When both are opened, The time taken to fill the cistern is:1. 80 min2. 70 min3. 60 min4. 48 min

Answer» Correct Answer - Option 2 : 70 min

Given:

A pipe can fill a cistern in 20 minutes.

Time taken by the leak to empty the tank = 28 minutes.

Concept used:

If a pipe can fill a tank in x hours then it can fill 1/x part of the tank in 1 hour.

Calculation:

Let the time taken by a pipe to fill the tank when the leakage arises be 1 minutes is 1/20 part.

And the time taken by a pipe to empty the tank be 1 minutes is 1/28 part.

When both pipes are opened,

The tank fills in 1 minute = 1/20 - 1/28

⇒ (7 - 5)/140

⇒ 2/140

⇒ 1/70 part

∴ The time taken to fill the tank is 70 minutes.

Discussion

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