How long for the same kob alone

Question

One person proofreads copy for a small newspaper in 4 hours. If a second proofreader is also employed, the job can be down in 2 1/2 hours. How long does it take for the second proofreader to do the same job alone?

Answer 1

Let x = time it takes for the second proofreader to do the job alone

 

1/x = amount of job done by second proofreader per hour

1/4 = amount of job done by first proofreader per hour

1/(2.5) = 2/5 = amount done per hour if they both work together

 

1/4 + 1/x = 2/5

 

Multiply the equation by the LCD, 20x, to obtain:   5x + 20 = 8x

 

                                                                           3x = 20

 

                                                                            x = 6 2/3 hr

Answer 2

First person reads at 1 newspaper/4hours

Second person reads at 1 newspaper/xhours

 

The average of they both is 1 newspaper/2.5hours

 

So, (1/4 + 1/x)/2=1/2.5

((x+1)/4x)/2=2/5

(x+1)8x=2/5

(x+1)*5=2*8x

5x+5=16x

5=16x-5x

5=11x

x=5/11

 

So, second person read at 1 newspaper every 5/11 hours. It's the same that saying 11 newspaper every 5 hours or 2.2 newspapers every hour.