Tim has employed Kathy and Leslie as bricklayers for the summer. Chris wants a brick wall built between his diving pool and the main swimming pool. Tim estimates that Leslie could build the wall in 9 hours and Kathy could build it in 10. However, he has learned that when they work together their combined output decreases by 10 bricks per hour. But, being in a hurry, he puts them both to work on it and finds that it takes them exactly 5 hours, working together, to finish the wall. How many bricks are in the wall?
