LAYING BRICKS!
Alex the Red estimated that one of his two bricklayers, Mustang Sally, would take 9 hours to build a certain wall and the other, Sandra Dee, 10 hours. However, he knew from experience that when they worked together, 10 fewer bricks got laid per hour. Since Alex the Red was in a hurry, he put both women on the job and found it took exactly 5 hours to build the wall. How many bricks did the wall contain?