Problema Solution
A roofer and an assistant can repair a roof together in 5 hours. Working alone, the assistant can complete the repair in 18 hours. If both the roofer and the assistant work together for 3 hours and then the assistant is left alone to finish the job, how much longer should the assistant need to finish the repairs? (Round your answer to one decimal place.)
Answer provided by our tutors
alone, the assistant can complete the repair in 18 hours so his rate is 1/18 roofs per hour
they work together 3 hours thus they will finish 3/5 of the job together and the assistant will have 1 - 3/5 = 2/5 of the job to finish alone
let t= the hours the assistant needs to finish 2/5 of the roof
rate of the assistant * t = 2/5 of the roof
(1/18)*t = 2/5
t = 7.2 hours
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the assistant will work 7.2 hours longer to finish the repairs.