Every week, Kate plays tennis for two hours, and her grade on each math test is 70 percent. Last week, after playing for two hours, Kate considered playing for another hour. She decided to play for another hour and cut her study time by one hour. But last week, her math grade fell to 60 percent. Use this information to work Problems 1 to 4.

1. What was Kate’s opportunity cost of the third hour of tennis?

2. Given that Kate played the third hour, what can you conclude about her marginal benefit and marginal cost of the second hour of tennis?

3. Was Kate’s decision to play the third hour of tennis rational?

4. Did Kate make her decision on the margin?