Time and Work Problem - Manhattan Test

[mpvader]

Bruce lays 200 bricks an hour and Wayne lays 300 bricks an hour, each working at a constant rate.

Quantity A

The time needed for Bruce to lay 700 bricks

Quantity B

The time needed for Bruce and Wayne, working together at their respective constant rates, to lay 1,700 bricks



The answer should be A.
If Bruce and Wayne work together, in 1 hr they can build
(1/200 + 1/300) bricks = (1/120) bricks
1700 bricks can be built in = 1700/120 hours.
But, in the test solution , the answer given when they work together is = 1700/500 hours.
Could you please tell me which is correct?

[tommywallach]

Hey MPV,

I'm not sure why you're changing 200 bricks an hour to 1/200 bricks an hour! If you make 200 bricks per hour, that's your rate, not 1/200th.

These two guys make 500 bricks per hour when they work together (one of them makes 200, and the other makes 300).

So if R * T = W:

500 * T = 1700

T = 1700/500 = 17/5

Hope that helps!

-t