Confidence Interval for when is known

When we do not know the population standard deviation we must use a different distribution to compute the error.

1. Use the sample standard deviation of s.
2. Use the student t- distribution with a specified degree of freedom, df = n-1, to find the critical cut off t-value,t_/2.
3. Find margin of error with the formula E= _{t/2. 8/N}
4. The confidence interval is x-E <

1. A random sample of 100 movie theaters showed mean price of a movie was $12.50 with a sample standard deviation of $0.80. Construct a 99% confidence interval for the population mean .

2. A sample of 8 cans are measured to find out how much soda they contain. The results are as follow:

12.

12

11.9

12.1

11.8

12

12.3

Construct a 95% confidence interval for the mean. The label on the side says 12oz. The sample standard deviation is 0.1574. Is this accurate?