phoenix9801 wrote:Anne can paint a certain house in 1/2 the time it takes Mary to paint the same house. If they work together at their respective constant rates, how many hours will it take them to paint the house if Anne can paint the house by herself in 3 hours?
A) 0.5
B) 1
C) 1.5
D) 2
E) 3
Let the house = 6 units.
Since Anne takes 3 hours to paint the house -- 1/2 the time it takes Mary -- Mary takes 6 hours to paint the house.
Rate for Anne alone = w/t = 6/3 = 2 units per hour.
Rate for Mary alone = w/t = 6/6 = 1 unit per hour.
When they work together, their combined rate = 2+1 = 3 units per hour.
Time for A+M to paint the house together = w/r = 6/3 = 2 hours.
The correct answer is
D.
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