Final answer:
Out of 1,066 students at Maryville High School, 213 signed a no-smoking pledge and 355 promised to discuss the dangers of smoking, leaving 498 students who did not participate in the Great American Smokeout.
Step-by-step explanation:
The students at Maryville High School who didn't participate in the Great American Smokeout can be calculated by finding out the number of students who signed the pledge and those who promised to talk to someone about the dangers of smoking, then subtracting these numbers from the total student count.
Firstly, the total number of students is 1,066. One-fifth of students signed the pledge, so they amount to 1,066 / 5 = 213 students. A third of the students promised to talk about the dangers of smoking, which is 1,066 / 3 = 355 students.
To find the number of students who didn't participate, we simply subtract the sum of participants from the total: 1,066 - (213 + 355) = 1,066 - 568 = 498 students.
Therefore, 498 students at Maryville High School didn't participate in the Great American Smokeout.