algebra
posted by Marta .
Solve
A contractor finds that it takes a crew A 6 hours to construct a wall of a certain size. Crew B takes 8 hours to construct a wall of the same size. How long will it take if they work together?

rate of A crew = wall/6
rate of B crew = wall/8
combined rate = wall/6 + wall/8
= 7wall/24
time with combined rate = wall/(7wall/24)
= 24/7
= 3.428 hours
= 3hours, 25.7 minutes
(notice the effective calculation was 1 รท (1/6 + 1/8)
Respond to this Question
Similar Questions

Math
A roofing crew can roof a house in 10 hours. If a second crew was added, the job would take 6 hours. How long would it take the second crew to roof the house alone? 
algebra
A boat's crew rowed 13.5 miles downstream, with the current, in 1.5 hours. The return trip upstream against the current covered the same distance, but took 4.5 hours. Find the crew's rowing rate in still water and the rate of the current. 
math
A library crew can shelve books in six hours. Another crew can do the job in four hours. If the first crew begins and is joined by the second crew one hour later, how many hours will it take to finish the job? 
MATH NEED HELP!
I have four questions in one. 1. A library crew can shelve books in six hours. Another crew can do the job in four hours. If the first crew begins and is joined by the second crew one hour later, how many hours will it take to finish … 
Algebra
A boat's crew rowed 7.5 downstream,with the current, in 1.5 hours. The return trip upstream against the current,covered the same distance,but took 2.5 hours. Find the crew's rate in still water and the rate of the current. 
math
How many cement blocks are needed to construct a wall 0.5 ft. thick, 6 ft. high, and 60 ft. long if it takes 10 standard cement blocks to make 1 cubic foot of wall? 
Algebra
There is a water tank with a drain of an unknown size that is always open. There is a series of input pipes above it which are all the same size. When 4 pipes are on, it takes 6 hours to fill. When 3 pipes are on, it takes 10 hours … 
Algebra
It takes matt 9 hrs longer to build a wall than it takes chris. Working together they can build the wall in 20hrs. how long would it take each working alone to build the wall? 
Math
Alice takes 4 hours to paint a wall. With sam's help, they can paint the wall in 3 hours. Without help, how long would it take Sam to do the same thing? 
math
It takes 8 hours for one crew to clean an office building. It takes a second crew 10 hours to clean the same building. If the first crew works 2 hours and leaves and the second crew takes over to complete the job, how long will it …