One student can proofread a copy for the newspaper in 4 hours. if a second proofreader is also employed, the job can be done in 2.5 hours. how long does it take for the second proofreader to do the same job alone?

Question

kropot72 · Answer

The student who proofreads a copy in 4 hours can read 1/4 = 0.25 of the copy in 1 hour.
When two people are proofreading, 1/2.5 = 0.4 of the copy is read in one hour. Therefore the second proofreader reads 0.4 - 0.25 = 0.15 of the copy in 1 hour.
Now we can find the time for the second proofreader to do the same job alone by taking the reciprocal of 0.15:
$$\frac{1}{0.15}=?\ hours+minutes$$

kropot72 · Answer

@lior94 Are you there? Do you understand?

anonymous · Answer

yes, im here. 
i mot sure how you got .25 for the first reader though, could you explain please?

kropot72 · Answer

If the first reader takes 4 hours to read the copy, the reader will read a quarter of the copy in one hour. 
1/4 = 0.25