John can finish a job in 8 hours whereas Sally only needs 5 finish the job. How quickly can they finish the job if they are working together?
So if they work together, in one hour they can complete:
#1/8 + 1/5 = 5/40+8/40 = 13/40#
To complete a whole job will therefore take:
#40/13 = 39/13 + 1/13 = 3 1/13#hours
#60/13 = 52/13 + 8/13 = 4 8/13#minutes
#(8 * 60) / 13 = 480/13 = 36.bar(923076) ~~ 37#
So the total time for the job is:
#3#hours, #4#minutes and #37#seconds
First we need to make an assumption that John and Sally can work at the same rate together as they do individually. This is quite a large assumption and quite possibly untrue in real life. However, since we haven't been given any information to the contrary, we'll go with that.
Let the total amount of work in the job be
From the question we know:
Then their combined work rates will be