Use the Confidence Level and Sample Data to Find a Confidence

Multiple Choice

Use the confidence level and sample data to find a confidence interval for estimating the population µ.
-A random sample of 79 light bulbs had a mean life of $x = 400$ hours with a standard deviation of $\sigma = 28$ hours. Construct a 90 percent confidence interval for the mean life, $\mu$ , of all light bulbs of this type.

A) $393 < \mu < 407$
B) $394 < \mu < 406$
C) $395 < \mu < 405$
D) $392 < \mu < 408$