Asked by marithes esquivel

keith has to grind tha values on his mercedes. he estimates it will take him 8 hrs.. his friends joe and russ have done the samejob in 10 and 12 hrs. respectively. keith had worked for 2 hrs... joe for another half an hour alone and russ came along and together they finished the job. how long did it take them to finish?
Answered by Ms. Sue
Your <b>School Subject</b> is <u>Math</u>.

Also -- is Keith grinding VALVES or VALUES on his car?
Answered by drwls
Keith did 1/4 of the job is 2 hours. Then Joe did 1/20 of the job in 1/2 hour. By that time, the job is 5/20 or 1/4 done.

When you say "together they finished the job" I will assume that all three of them then finished the job together.

Together, they work at a combined rate
1/8 + 1/10 + 1/12 job/hour = (15+12+10)/120 = 37/120 job/hr

To finish the remaining 3/4 of the job, the time required is
(3/4)/(37/120) = 90/37 = 2.43 hours

If Joe and Russ finished the job together, their rate of work is 22/120 job/hr and the time required is
(3/4)/(22/120) = 90/22 = 4.09 hours
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