<PRE><B>Question 931553</B>
A roofer and an assistant can repair a roof together in 7 hours. Working alone, the assistant can complete the repair in 16 hours. If both the roofer and the assistant work together for 4 hours and then the assistant is left alone to finish the job, how much longer should the assistant need to finish the repairs?


A roofer and an assistant can repair a roof together in 7 hours. 
they together do 1/7 of the job in 1 hour

Working alone, the assistant can complete the repair in 16 hours.
Assistant can do 1/16 of the job in 1 hour

 If both the roofer and the assistant work together for 4 hours
So they do 4/7 of the job

So 1-4/7 = 3/7 of the job left over

1 job, assistant does in 16 hours
3/7 of the job he does in (3/7 * 16)

6.86 hours
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