One person proofreads copy for a small newspaper in 6 hours

One person proofreads copy for a small newspaper in 6 hours. If a second proofreader is also employed, the job can be done in 2 1/2 hours. How long does it take for the second proofreader to do the same job alone?

Solution

Given that

First profreader don the job = 6 hours

First profreader one hour\'s work = 1 / 6

Both profreaders done the job = 2 1/2 = 5 /2 hours

Both profreaders one hours work = 2 / 5

Second profreader done the same job alone in 1 hour = 2 /5 - 1/6

= 7 / 30

Therefore,

Second profreader done the same job alone = 30 / 7

= 4 2/7 hours