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18. A savings and loan association needs information concerning the checking account balances of its local customers. A random sample of 20 accounts was checked and yielded a mean balance of $782.16 and a standard deviation of $233.29. Assume the data are normally distributed. Find a 98% confidence interval for the true mean checking account balance for local customers. Show all work and state the following: Critical t or z score (label appropriately): Margin of Error: Write the confidence interval as indicated below, rounding values to the nearest cent. Confidence Interval: