Tap A can fill a tank in 6 minutes. After filling half of the tank 3 more similar taps opened in the tank. In what time the tank filled completely?

3 min 45 sec

A can fill the tank in - 6min

let capacity of the tank is 6 ltr

therefore, Efficiency of A = 1 ltr/min

Half tank i.e. 3 ltr will be filled in 3 min

Then,  three more pipes are open with the efficiency of 1 ltr/min

Now,

Remaining tank = 3 ltr

Efficiency working = 1 + 1 + 1 + 1 = 4 ltr/min

Time =\(\frac{3}{4}\) min = 45 sec

Total time = 3 min 45 sec.