The quality control manager at a light bulb factory needs to estimate the mean life of a large shipment of light bulbs. A random sample of 36 light bulbs indicated a sample mean life of 350 hours. The standard deviation of the sample is 100 hours.

Construct a 99% confidence interval estimate for the population mean life to light bulbs in this shipment.

Step 1: figure out a point estimate:

Step 2: Is (population standard deviation) known? If no, then find sample size nand s/n

---Here s is the sample standard deviation.

Step 3: find the confidence level (1-) and the critical value t_{(1-/2, n-1)}.

Step 4: construct a confidence interval for population mean. Please interpret the confidence interval.

2. If you want to be 95% confident of estimating the population mean to within a sampling error of +1.5 and the standard deviation is assumed to be 10, what sample size is required?