Hypothesis testing: state the hypotheses, is there evidence that the claim is not valid?

The purchase of a coin-operated laundry is being considered by a potential entrepreneur. The present owner claims that over the past 5 years the average daily revenue has been $675 with a standard deviation of $75. A sample of 30 selected days reveals a daily average revenue of $625.

a. State the null and alternative hypothesis
b. Is there evidence that the claim of the present owner is not valid? (use a .01 level of significance.)
c. What will your answers be in (b) if the standard deviation is now $100?
d. What will your answer be in (b) if the sample mean is $650?

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