Answer: a. 69.72 ± 1.37
Step-by-step explanation:
We want to determine a 90% confidence interval for the mean height (in inches) of adult men in the United States.
Number of sample, n = 25
Mean, u = 69.72 inches
Standard deviation, s = 4.15
For a confidence level of 90%, the corresponding z value is 1.645. This is determined from the normal distribution table.
We will apply the formula
Confidence interval
= mean ± z × standard deviation/√n
It becomes
69.72 ± 1.645 × 4.15/√25
= 69.72 ± 1.645 × 0.83
= 69.72 ± 1.37
The lower end of the confidence interval is 69.72 - 1.37 = 68.35
The upper end of the confidence interval is 69.72 + 1.37 = 71.09
