Question

Confidence Interval The quality-control manager at a light bulb factory needs to determine whether the mean life of a large shipment of light bulbs is equal to 375 hours. The population standard deviation is 120 hours. A random sample of 64 light bulbs indicates a sample mean life of 350 hours.

1. At the 95% confidence level, what is the critical value? 39. What is the confidence interval based on this data?

2. Is there evidence that the mean life is different that the claim of 375 hours?

3. What would the confidence interval be if we used a sample of 100 light bulbs.

4. What would the interval be if we used a .1 level of significance for the data above (sample size = 64)?

5. Explain the difference between your answer in 2 and 5.

Answer 1