Question

A random sample of 118 light bulbs had a mean life of hours with a standard deviation of hours. Construct a 90 percent confidence interval for the mean life, μ, of all light bulbs.

Answer 1

444 < µ < 454

Explanation:

Confidence interval is:

CI = µ ± CV × SE

where CV is the critical value and SE is the standard error.

For a 90% confidence, CV = z = 1.645.

The standard error is:

SE = σ/√n

SE = 33/√118

SE = 3.04

So the confidence interval is:

CI = 449 ± (1.645) (3.04)

CI = 449 ± 5

444 < µ < 454