Question

Two mechanics were working on your car. One can complete the given job in six hours, but the new guy takes eight hours. They worked together for the first two hours, but then the first guy left to help another mechanic on a different job. How long will it take the new guy to finish your car?

Answer 1

3 1/3 hours

Explanation:

In 2 hours, the first guy did 2/6 = 1/3 of the job. Meanwhile, the new guy did 2/8 = 1/4 of the job. When the first guy left, the remaining amount of the job was ...

1 - 1/3 - 1/4 = 12/12 -4/12 -3/12 = 5/12 . . . . . fraction of job remaining

So, completion of the remaining 5/12 of the job will take the new guy ...

(5/12)(8 hours) = 10/3 hours = 3 1/3 hours