SOLUTION: Tom is painting the set for a school play. Working alone, he could finish the job in 12 hours. His friend Brad could paint the set in 8 hours. Tom and Brad begin working togethe

Algebra ->  Rate-of-work-word-problems -> SOLUTION: Tom is painting the set for a school play. Working alone, he could finish the job in 12 hours. His friend Brad could paint the set in 8 hours. Tom and Brad begin working togethe      Log On


   

Question 608078: Tom is painting the set for a school play. Working alone, he could finish the job in 12 hours. His friend Brad could paint the set in 8 hours. Tom and Brad begin working together, but after 3 hours, Brad leaves. How many more hours will tom need to work to finish the set?
Answer by ewatrrr(24785) About Me  (Show Source):
You can put this solution on YOUR website!
 

Hi

Tom in 12 hours...His friend Brad could paint the set in 8 hours

Let x represent time to finish the Entire set together

Per Hour KEY:

 1/12 + 1/8 = 1/x

   8x + 12x = 96

       20x = 96

         x = 4.8 hr, 

% of work w done together in 3 hr

         1/4.8 = w/3

            3 = 4.8w

            3/4.8 = .625 = w

How many more hours h will tom need to work to finish the set

 1/12 = .625/h

   h = 12(.625)= 7.5 more hours