Asked by Victoria
Q1: Robert can paint a room in 12 hours. Dennis and Vince can paint the room in 10 hours & 9 hours respectively. If Dennis and Vince work together for 2 hours, How long will it take Robert to finish the job? I think it's 12 (because it says it, but I think the question was how could he do it if he worked together? I'm not sure.), but I'm unsure of my answer so please explain.
Answers
Answered by
Steve
How much of the job gets done in one hour by each person?
Robert: 1/12
Dennis: 1/10
Vince: 1/9
So, in 2 hours, Dennis and Vince can do
2/10 + 2/9 = 19/45 of the job
That leaves 26/45 for Robert to do. At his rate of 1/12 per hour, it will take him
(26/45)/(1/12) = 6.933 hours or 6 hr 56 min
Robert: 1/12
Dennis: 1/10
Vince: 1/9
So, in 2 hours, Dennis and Vince can do
2/10 + 2/9 = 19/45 of the job
That leaves 26/45 for Robert to do. At his rate of 1/12 per hour, it will take him
(26/45)/(1/12) = 6.933 hours or 6 hr 56 min
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