Questions: A study of several cities shows a positive correlation between the percent of people who swim outdoors and the number of barbecue grills sold. Which statement is most likely true? Swimming makes people hungry for a barbecue. The correlation is due to a third variable: cost of milk. Barbecuing makes people want to swim. The correlation is due to a third variable: weather.

The answer is: The correlation is due to a third variable: weather.

Explanation for each option:

1. Swimming makes people hungry for a barbecue.

   • This statement suggests a direct causal relationship between swimming and barbecuing. While it is possible that people might feel hungry after swimming and decide to have a barbecue, this does not explain the overall correlation observed across several cities. It is more likely that another factor influences both activities.

2. The correlation is due to a third variable: cost of milk.

   • This option is unlikely because the cost of milk does not have a clear, logical connection to either swimming outdoors or the number of barbecue grills sold. There is no evident reason why changes in milk prices would affect these two activities.

3. Barbecuing makes people want to swim.

   • Similar to the first option, this statement implies a direct causal relationship, but in the opposite direction. While it is conceivable that people might want to swim after barbecuing, this does not sufficiently explain the correlation observed across multiple cities.

4. The correlation is due to a third variable: weather.

   • This is the most plausible explanation. Weather conditions, particularly warm and sunny weather, are likely to encourage both outdoor swimming and barbecuing. Therefore, the positive correlation between the percent of people who swim outdoors and the number of barbecue grills sold can be attributed to favorable weather conditions that promote both activities.