Hi All,

We're told that Jason can stack 2 shelves in 3 hours and Maria can stack 3 shelves in 2 hours. We're asked how long will it take them together, working at their constant rates, to stack thirteen shelves. This question is a 'rate' question, so you can work through the math in a number of different ways. Here's an approach that puts both rates in terms of 'output per hour':

Jason stacks 2 shelves every 3 hours, so he stacks 2/3 of a shelf per hour.
Maria stacks 3 shelves every 2 hours, so he stacks 3/2 of a shelf per hour.
Combined, they stack 2/3 + 3/2 = 4/6 + 9/6 = 13/6 shelves per hour.

We're asked how long it would take for the two to stock 13 shelves....

(X)(13/6 shelves/hour) = 13 shelves
X = 13(6/13) = 6 hours

Final Answer: B

GMAT assassins aren't born, they're made,
Rich