Question

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?

Answer 1

Answer:

   3 hours, 4 minutes and 37 seconds

Step-by-step explanation:

In 1 hour, John will complete 18 of a job and Sally 15.

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 $\frac{1}{13}$ hours

In minutes, $\frac{1}{13}$ hour is:

   60/13 = 52/13 + 8/13 = 4 $\frac{8}{13}$ minutes

In seconds, $\frac{8}{13}$ minutes is:

   (8 * 60)/13 = 480/13 = 36.923076 ≈ 37

So the total time for the job is:

   3 hours, 4 minutes and 37 seconds