Lisa, an experienced shipping clerk, can fill a certain order in 8 hours. Bill, a new clerk, needs 9 hours to do the same job.

Question

Working together, how long will it take then to fill the order. The solution is _ hours

Answer 1

Hourly rates are 1/8 of job per hr for her, 1/9 for him.

t(1/8 + 1/9) = 1

solve for t, hours for the whole job(1) to be accomplished by their working together.