The Smith painting company is to paint an exterior wall with four identical walls. The first wall is painted by the master painter himself. This work takes him two hours. Meanwhile, the apprentice paints the second wall. Since he is not yet as experienced, he takes twice as long as his master, who also paints the third wall in this time.
To finish the job quickly, the two decide to paint the last wall together after their lunch break.
How long will it take them together to completely paint the last wall?
Since the master works twice as fast as the apprentice and they both work the same amount of time, the master paints 2/3 of the wall and the apprentice paints 1/3.
It takes the master 2/3 of 120 minutes to paint 2/3 of the wall. So together they will take 80 minutes to paint the entire wall.