Question

A consumer activist group wants to determine the mean lifetime of the Amazon Kindle DX. The consumer activist groups randomly selects 25 Kindles and finds that the average lifespan was 38 months with standard deviation 12 months. Find a 95% confidence interval for the population mean lifetime of the Amazon Kindle DX.

Answer 1

Confidence interval for the population mean lifetime of the Amazon Kindle DX is (33.30 months to 42.70 months)

Explanation:

Given;

Mean lifespan x = 38 months

Standard deviation r = 12 months

Number of kindle selected n = 25

Confidence range = 95%

Z*(95%) = 1.96

Confidence interval = x+/-Z*(r/√n)

= 38 +/- 1.96(12/√25)

= 38 +/- 4.70

Confidence interval = (33.30 months to 42.70 months)