An unconfined compression test was performed to determine the average strength of concrete cylinders (in psi). It is believed that the strength is approximately normally distributed with a standard deviation of 256 psi. A sample of 70 concrete cylinders was taken, and it was found that the average strength was 3000 psi. Find a 91% confidence interval for the true average strength of the concrete. Be sure to:

• State the value for α.
• State whether you should use z or t and find the appropriate value. Round z-values to 2 decimals. Round t-values to 3 decimals.
• Find the confidence interval (to 2 decimals). State the parameter your confidence interval is for.
• Write a verbal interpretation of your confidence interval.