Your School Subject is Math.
Also -- is Keith grinding VALVES or VALUES on his car?
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?
2 answers
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
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
1 answer