AAPL wrote:Magoosh
Jason can stack two shelves in 3 hours and Maria can stack three shelves in 2 hours. How long will it take them together, working at a constant rate, to stack thirteen shelves?
A. 5 hours
B. 6 hours
C. 6.5 hours
D. 11 hours
E. 12 hours
Let each shelf = 6 pounds.
Since Jason takes 3 hours to stack 2 6-pound shelves -- for a total of 12 pounds -- Jason's rate = 12/3 = 4 pounds per hour.
Since Maria takes 2 hours to stack 3 6-pound shelves -- for a total of 18 pounds -- Maria's rate = 18/2 = 9 pounds per hour.
Total weight of 13 6-pound shelves = 13*6 = 78 pounds.
Combined rate for Jason and Maria = 4+9 = 13 pounds per hour.
Time for Jason and Maria to stack the 13 shelves = 78/13 = 6 hours.
The correct answer is
B.
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