Construct a 90% confidence interval for the population mean. Assume the population has a normal distribution. A same of 15 randomly selected math majors has a grade point average of 2.86 with a standard deviation of 0.78. Round to the nearest hundredth.

Question

Answers:
a) (2.41,3.42)
b) (2.28, 3.66)
c) (2.51, 3.21)
d) (2.37, 3.56)

Answer 1

90% = mean ± Z (SEm)

SEm = SD/√n

Find table in the back of your statistics text labeled something like "areas under normal distribution" to find the proportion/probability (p = ±.05) and its Z score. Insert data into first equation.

Answer 2

CI=2.86 ± 1.76*0.78/√15
=2.86 ± 0.3545

c) (2.51, 3.21)