Raghu’s tanker can fill a cistern in 4 hours. After half the cistern is filled, three more similar tankers are opened. Whatis the total time taken to fill the cistern completely?

A tap can fill a tank in 4 hours

=> The tap can fill half the tank in 2 hours

Remaining part = $$\frac{1}{2}$$

After half the tank is filled, three more similar taps are opened.

Hence, total number of taps becomes 4.

Part filled by one tap in 1 hour =  $$\frac{1}{4}$$

Part filled by four taps in 1 hour = $$4\times \frac{1}{4}$$=1

i.e., 4 taps can fill remaining half in 30 minutesPart filled by one tap in 1 hour = $$\frac{1}{4}$$



Total time taken = 2 hour + 30 minute = 2 hour 30 minutes