Question

A company has two large computers. The slower computer can send all the company's email in 55 minutes. The faster computer can complete the same job in45 minutes. If both computers are working together, how long will it take them to do the job?

Answer 1

You find the rates of each computer on its own...

One does the job in 55 minutes which we can say is 1/55

The other has a rate of 1/45.

The question wants to know how long it would take both working simultaneously to complete the job...

t/55+t/45=1

(9t+11t)/495=1

20t=495

t=24.75 minutes   (24:15)