The average life of light bulbs produced by SABA Electric Co

The average life of light bulbs produced by SABA Electric Co. is believed to be normally distributed with the mean service life of 920 hours and a standard deviation of 100 hours. A random sample of 100 bulbs is tested and it has a mean life of 905 hours. Can it be concluded that the mean service life of the bulbs is less than the expectation at 1% level of significance?

A. Yes. The mean service life of the bulbs is less than the expectation.

B. No. The mean service life of the bulbs is not less than the expectation.

C. No. The mean service life of the bulbs is more than the expectation.

D. None of the above.

Solution