Bricklayer Brenda would take 9 hours to build a chimney alone, and bricklayer Brandon would take 10 hours to build it alone. When they work together, they talk a lot, and their combined output is decreased by 10 bricks per hour. Working together, they build the chimney in 5 hours. How many bricks are in the chimney?

(A) 500
(B) 900
(C) 950
(D) 1000
(E) 1900
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Brenda can do 1/9th of the work in 1 hr and Brandon can do 1/10th of the work in 1 hr.
Working together they can do (1/9+1/10)=19/90th of the work in 1 hr which means that together they can complete the work in 90/19 hours.
Now let the total number of bricks in the chimney be 'x'.
So had they worked at their usual speed (without wasting time by gossiping) they would would have laid 'x/(90/19)'=19x/90 bricks in 1 hr. But they did gossip and ended up finishing the work in 5 hours which means that they laid x/5 bricks in an hour.
We are told that their combined output decreased by 10 bricks/hr due to the time they wasted.

Thus, 19x/90 - x/5 = 10. Solving we have x=900. Ans.: B