Working together, it takes two computers 5 minutes to send out a company's email. If it takes the slower computer 15 minutes to do the job on it's own, how long will it take the faster computer to do the job on it's own?

The answer is 6 minutes.

In principal to more is less in division and in multiplication more than 1 numbers are expected to increase.

As shown here;

15 mins = 15/2.5 = 6 , 15 separately.

5 mins = 2 5 + 2.5 = 5 combined

If the other computer has a same rate of decrease then we can subtract 15-2.5 = 12.5 and find the average of 6.25.

good luck!

cutie~