Question

The average life of light bulbs produced by SABA Electric Co. is believed to be normally distributed with the mean service life of 950 hours and a standard deviation of 100 hours. A random sample of 100 bulbs is tested and it has a mean life of 930 hours.

Can it be concluded that the mean service life of the bulbs is less than the expectation at significant level of 0.01?
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. Both a and b are correct.
D. None of the above

×

Answer 1

The test statistic here is computed as:

Now from standard normal tables, we get here:
P(Z < -2) = 0.023

As the p-value here is 0.023 > 0.01 which is the level of significance, therefore the test is not significant and we cannot reject the null hypothesis here. Therefore B is the correct answer here.