Answer to Question 1
A person's IQ and his or her telephone number are likely to show zero correlation. The number of winter coats sold and the temperature outside are likely to show a negative correlation. The quantity of fertilizers used and crop yield (e.g., the number of bushels of wheat grown per acre) are likely to have a positive correlation.
Answer to Question 2
When marginal cost is lower than average total cost, average total cost is falling. When marginal cost is greater than average total cost, average total cost is rising. When marginal cost is equal to average total cost, average total cost is at its minimum.