Two pipes, A and B, can fill a tank in 12 minutes and 15 minutes respectively. Both pipes are opened simultaneously, but pipe A is closed after 3 minutes. How much additional time will pipe B require to fill the tank completely?

Explanation

Pipe A fills 1/12 of the tank per minute, and pipe B fills 1/15 per minute. In the first 3 minutes, both run together, filling (3 × 1/12) + (3 × 1/15) of the tank. After that, only pipe B continues to fill the remaining part at 1/15 per minute. Setting up the equation: (3/12) + (3/15) + (x/15) = 1, solving for x gives x = 8 1/4 minutes.