The idea that as the quantity of an input increases, the additional output decreases (holding all else constant is called the law of answer.

When the national economy goes from bad to better, market research shows changes in the sales at various types of restaurants. projected 2011 sales at quick-service restaurants are $164.8 billion, which was 3% better than in 2010. projected 2011 sales at full-service restaurants are $184.2 billion, which was 1.2% better than in 2010. how will the dollar growth in quick-service restaurants sales compared to the dollar growth for full-service places?