A mason can build a retaining wall in 10 hours.

Question

A mason can build a retaining wall in 10 hours. With his apprentice assisting, the wall is built in 6 hours. How long would it take the apprentice alone to construct the wall?

Answer 1

1 / 10      how much of the job the mason can do in one hour

6 / 10      how much of the job the mason does with the apprentice.

 

1 / x        how much of the job the apprentice does in one hour

6 / x        how much of the job the apprentice does with the mason

 

6/10 + 6/x = 1                1 because they complete 1 job

(6x + 60) / 10x = 1

6x + 60 = 10x

60 = 4x

15 = x

 

Working alone the apprentice would need 15 hours to complete the job.