Question 104888
Combined work efforts are similar to mixture problems. You need to figure out the "pure" rate of work per hour by each person.

In this case, Bill takes 2 hr to do 100% of the job, so he does 50% per hr.
In contrast, Monica does 100% of the job in 1 hr, so she does 100% per hr.

Working together they do the full job.

.5x +x = 1

1.5x = 1
x = 1/1.5 = 2/3 hr

ALWAYS check:
2/3*.5 = 1/3 = Bill's contribution
2/3*1 = 2/3 = Monica's contribution
1/3 +2/3 = 1 =full job.
Check.