A tank is fitted with two taps. The first tap can fill the tank completely in 45 minutes and the second tap can empty the full tank in one hour. If both the taps are opened alternately for one minute, then in how many hours the empty tank will be filled completely ?

Correct Answer: 5 hours 53 minutes

1/45-1/60 = 4-3/180

In first minute A fill 4 units of water

In second minute B empty 3 units of water

After two minutes tanks has 1 units of water.

Note: Decrease the higher value i.e 4 from total capacity 180−4=176 units.

1 unit filled in 2 minutes

176 units filled in 352 minutes

Now in next minutes pipe A will fill 4 units. And tank is full so total time taken is 352+1=353

minutes or 5 hour 53 minutes