Working alone, carol can paint 1 room in 4 hours. david, working alone, can paint the same sized room in 6 hours. if they work together, how long would it take them to paint that sized room?

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The Russ' rate of work is of the job per minute. After he had been working for 15 minutes, he had done = of the job; Hence, of the job remained. Then Russ and Joe completed the work in 10 minutes; hence, their combined rate of work was = of the job per minute. It means that the Jay's individual rate of work was the difference - = - = of the job per minute. Therefore, it would take Jay minutes = 26 minutes and 40 seconds to complete the job working alone.