In the first two weeks of school, Jill studied 13 hours each week. How many hours must she study during the third week to have an average of 15 hours per week?

Jill needs to study 19 hours during the third week to reach an average of 15 hours per week, calculated by setting up an equation based on her previous study hours and solving for the third week.

Explanation:

To find out how many hours Jill must study during the third week to achieve an average of 15 hours per week, we can set up an equation. Given that Jill studied 13 hours in each of the first two weeks, we can express the total hours studied over three weeks as 13 + 13 + x, where x is the number of hours she needs to study in the third week. To find the average, we divide the total hours by 3 (the number of weeks), which we want to equal 15 hours.

Solving the equation:

13 (first week) + 13 (second week) + x (third week) = total hours studied
(13 + 13 + x) / 3 = 15
26 + x = 45
x = 19 hours

Therefore, Jill must study 19 hours during the third week to average 15 hours per week.