a. Notice that as the temperature in the summer goes up, so does the amount of ice cream sold.
Therefore, there is a directly proportional relationship between the temperature in the summer and amount of ice cream sold.
b. As the incident of vaccination in a city goes up, the number of ill people goes down.
This way, we can say that there is an inversely proportional relationship between the incident of vaccination in a city and incidence of illness in that city.
