Question

Working together, it takes two computers 15 minutes to send out a company's email. If it takes the slower computer 60 minutes to do the job on its own, how long will it take the faster computer to do the job on its own? Do not do any rounding.

Answer 1

Let x = time (minutes) it takes for the faster computer to do the job alone
then
12(1/30 + 1/x) = 1
multiplying both sides by 30x:
12(x + 30) = 30x
12x + 360 = 30x
360 = 18x
20 minutes = x