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
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.
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