Economists often compare variables to determine the nature and extent of their relationships so that they can anticipate outcomes from changes in related variables. The relationship can be positive or negative. For example, the number of hours of exercise and a person's blood sugar count has a negative relationship. Describe a pair of economic variables with a positive relationship and a pair with a negative relationship. Explain the extent to which they change in response to each other and the importance of their relationship to economics. Focus on "economic" variables only. (one paragraph)