Question 1205973
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It takes Leon 17 hours to seal his driveway working by himself. 
If Michael helps​ Leon, they can seal the driveway in 5 hours. 
How long would it take Michael to seal the driveway​ alone?
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Their combined rate of work is 1/5 of the job per hour.

Leon's rate of work is 1/17 of the job per hour.

Hence, Michael's rate of work is the difference

    {{{1/5}}} - {{{1/17}}} = {{{17/85}}} - {{{5/85}}} = {{{12/85}}}  of the job per hour.


It means that Michael needs  {{{85/12}}} = 7{{{1/12}}} hours = 7 hours and 5 minutes

to complete the job working alone.


<U>ANSWER</U>.  Michael needs  7 hours and 5 minutes to complete the job working alone.
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Solved.