Question

a group of 8th and 9th graders were surveyed about whether they use social media to communicate with their friends. the results are shown below in the conditional relative frequency table by row.

	do not use	use	total
9th grade	0.19	0.81	1.00
total	0.38	0.62	1.00

which conclusions can be drawn from the results of the survey? check all that apply.

• there is no association between using social media and grade level.
• the probability a student uses social media, given that he or she is in 9th grade, is 81%.
• a student who is more likely to not use social media is in 8th grade.
• an 8th grader is more likely to use social media than not.
• knowing a students grade level does not help determine if he or she uses social media.

Explanation:

1. "There is no association between using social media and grade level": Compare the conditional relative frequencies for "Use" in 8th (0.84) and 9th (0.81) grades. Since they differ, there is an association. So this is false.
2. "The probability a student uses social media, given that he or she is in 9th grade, is 81%": From the table, the "Use" row for 9th grade is 0.81 (or 81%). This is true.
3. "A student who is more likely to not use social media is in 8th grade": Compare "Do Not Use" frequencies: 8th (0.16) and 9th (0.19). 0.19 > 0.16, so 9th graders are more likely to not use. This is false.
4. "An 8th grader is more likely to use social media than not": For 8th grade, "Use" is 0.84 and "Do Not Use" is 0.16. 0.84 > 0.16, so this is true.
5. "Knowing a student's grade level does not help determine if he or she uses social media": Since the conditional frequencies for "Use" differ by grade (0.84 vs. 0.81), grade level does help. This is false.

Answer:

• The probability a student uses social media, given that he or she is in 9th grade, is 81%.
• An 8th grader is more likely to use social media than not.