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 its own, how long will it take the faster computer to do the job on its own?
Do not do any rounding.
Let the time it takes the faster computer to do the job on its own be x minutes.
When working together, the rate at which they complete the job is 1/5 of the job per minute.
The slower computer's rate is 1/15 of the job per minute.
The faster computer's rate is 1/x of the job per minute.
When working together:
1/15 + 1/x = 1/5
Multiplying through by 15x:
x + 15 = 3x
15 = 2x
x = 7.5 minutes
Therefore, it will take the faster computer 7.5 minutes to do the job on its own.