Question

6) A random sample of high school girls were asked how many hours per week they use social media. The sample mean of the 25 girls was 9 with standard deviation 2.7. What is the 90% confidence interval for the true mean for the hours per week high school girls use social media? Assume the population is normally distributed.

Answer 1

n=25, = 9, s=2.7, c=90%

Now formula for confidence interval is

Where tc is the t critical value for c=90%

with df= n-1 = 25 -1 = 24

Using t table we get critical value as

tc= 1.711

Now put in formula

8.0761 < < 9.9239

Therefore we are 90% confident that the true mean for the hours per week high school girls use social media

lies between 8.0761 to 9.9239