Problem Solving

swerve wrote: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

The OA is B

Source: Magoosh

Given that Jason can stack two shelves in 3 hours, he can stack 13 stacks in 3/2*13 = 39/2 hours and Maria can stack three shelves in 2 hours, she can stack 13 stacks in 2/3*13 = 26/3 hours

Working together they together stack 13 shelves in reciprocal of [1/(39/2) + 1/(26/3)] hours = reciprocal of 13/78 = 6 hours

The correct answer: B

Hope this helps!

-Jay
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swerve wrote: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

The OA is B

Source: Magoosh

The combined rate of Jason and Maria is 2/3 + 3/2 = 4/6 + 9/6 = 13/6.

So it takes them 13/(13/6) = 13 x 6/13 = 6 hours to stack 13 shelves.

Answer: B