Question

A new photocopier works 4 times as fast as an old one. When the machines work together, a university can produce all its staff manuals in 28 hours. Find the time it would take each machine, working online, to complete the job.

Answer 1

The old photocopier can make x manuals in an hour. The new photocopier can make 4x. Combined, they made 5x manuals in an hour.

In one hour they can make 1/28 of the manuals.

1/(28*5)=1/140 is the rate.

The new photocopier can make all the manuals in 4/140 or 35 hours.

The old one can make them in 140 hours.