SOLUTION: 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 wi

Algebra ->  Rate-of-work-word-problems -> SOLUTION: 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 wi      Log On


   

Question 819762: 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 for the job to be completed?
Answer by josmiceli(19441) About Me  (Show Source):
You can put this solution on YOUR website!
Library crew's rate of working:
+1%2F6+
Fraction of the job done in 1 hour by library crew:
+%28+1%2F6+%29%2A1+=+1%2F6+
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+1+-+1%2F6+=+5%2F6+ is the fraction left to be
finished by both crews
Let +t+ = time in hours to finish the job
+1%2F6+%2B+1%2F4+=+%28%285%2F6%29%29+%2F+t+
+1%2F6+%2B+1%2F4+=+5%2F%286t%29+
Multiply both sides by +12t+
+2t+%2B+3t+=+10+
+5t+=+10+
+t+=+2+ hrs
The job takes +1+%2B+2+=+3+ hrs to complete