Charity Run Distance Calculation

David is participating in a charity run. He plans to run a total distance of 15 kilometers over 3 days. On the first day, he runs 5 kilometers. On the second day, he runs X kilometers. If he wants to average the same distance each day, how many kilometers does he need to run on the third day?

To find out how many kilometers David should run on the third day, first determine how many kilometers he has left to reach his goal after completing the first two days. His average goal is to run the total distance divided by the number of days, which is $$ \f\frac{15 \text{ kilometers}}{3} = 5 \text{ kilometers} $$ per day.