Question

joe and Bill are working on building a stone wall that will be 120 feet long. Joe works from one end and is able to build one ten foot section in 5 hours. Bill starts from the other end and is able to finish a ten foot section in 4 hours. How long will it take Joe and Bill to finish building the wall?

Answer 1

26 hours to complete the wall

Answer 2

Joe completes an average of (10 ft)/(5 h) = 2 ft/hour. Bill completes an average of (10 ft)/(4 h) = 2.5 ft/hour. Together, they complete 2+2.5 = 4.5 ft/hour. At that rate, it will take them

... (120 ft)/(4.5 ft/h) = 26 2/3 h