A manager of the credit department for an oil company would like to determine whether the average monthly balance of credit card holders is greater than $75. An auditor selects a random sample of 25 accounts and finds that the average owed is $ 83.40 with a sample standard deviation of $ 11.83. Test using a 5% level of significance whether the average balance is more than $ 75. (Ans: H0:=75 against H1: >75 and reject H0