Question

An electrical firm manufactures light bulbs that have a length of life that is approximately normally distributed with a standard deviation of 40 hours. If a sample of 30 bulbs has an average life of 780 hours, construct a 96% confidence interval for the population mean of all bulbs produced by this firm.

Identifying all the required quantities correctly from problem statement = 5 points

Sketch the probability/ area on normal PDF curve = 5 points

Calculate the z value from Z tables = 5 points

Construct the required Confidence interval = 5 points

(Partial credit if steps are not shown)

Answer 1