Jane can paint the office by herself in 7 hours. Working with an associate, she can paint the office in 3 hours. How long would it take her associate to do it working alone?
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Let’s suppose that her associate would be able to paint the office alone in x hours.
If Jane can paint the office alone in 7 hours, it means that in one hour she paints 1/7 of the office.
If Jane and her associate can paint the office in 3 hours, it means that in one hour together, they can paint 1/3 of the office.
If Jane can paint 1/7 of the office in one hour, and together they can paint 1/3 of the office in one hour, that means that her associate can paint 1/3 - 1/7 = 7/21 - 3/21 = 4/21 of the office in one hour.
Therefore, her associate would take 21/4 hours or 5.25 hours to paint the office alone.
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