The Purplemath Forums

Assume a job is x. In 12 minutes, person A does x, and in 18 minutes, person B does x too. So, we'll view it in 1 minute. In 1 minute, essentially person A does x/12 minutes and person B does x/18 minutes. So if A and B does it together they do x/12 + x/18 of work. Simplifying the denominator, we we...