Question 394216
Evan, John, and Mark are on the same Learning Team at UOP. If each worked on the team assignments alone, it would take Evan 10 hours, John 8 hours, and Mark 12 hours to finish the assignments. 
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They usually started the same time on Monday night after work. But last week, Evan started early and he worked for 2 hours on the assignments when John and Mark began. Later, all three finished the team assignments. How long did they take to finish by working together?
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Evan rate: 1/10 job/hr
John rate: 1/8 job/hr
Mark rate: 1/12 job/hr
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Evan finished 2/10 of the job in 2 hrs.
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Equation:
Let "x" be time to finish the job together:
x[1/10+1/8+1/12] = 8/10 job
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x[(12 + 15 + 10)/120] = 8/10
x[37/120] = 8/10
x = (120/37)(8/10)
x = (12*8/37)
x = 2.59 hrs
x = 2 hr 35min 24sec
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Cheers,
Stan H.