Posted by Sara on .
A company has developed a new type of light bulb, and wants to estimate its mean lifetime. A simple random sample of 12 bulbs had a sample mean lifetime of 692 hours with a sample standard deviation of 30 hours. It is reasonable to believe that the population is approximately normal. Find the lower bound of the 95% confidence interval for the population mean lifetime of all bulbs manufactured by this new process.
Round to the nearest integer. Write only a number as your answer. Do not write any units.

Statistics 
Kuai,
692+ 1.96* 30 /sqrt(12)
692 + 16.97
(675, 709)