Question

Bob needs to send out a mailing for his company. Working alone, it will take him 10 hours to get the job done. Ellen can do the job in 8 hours by herself. They work together for 2 hours, and then Ellen finishes the job by herself. Which choice is the best estimate for how long the job will take in all?​

Answer 1

6 2/5 hrs or 6.4 hours total

Explanation:

In two hours, Bob completes 2/10 = 1/5 of the job

Ellen completes 2/ 8 = 1/4

Find amount left

1 - 1/5 -1/4 = 1 - 4/20 - 5/20 = 11/20 left

Ellen will need 8hrs * 11/20 = 88/20 = 4 2/5 hours to finish the job

2 hours to start + 4 2/5 hours to finish = 6 2/5 hours total