A local Vancouver health food store is gathering information about the income of their customers. They survey every customer and find that the average income of their customers is $50,000 / year with a standard deviation of $1,000. However, their general manager is unhappy with how expensive it was to survey every single customer. She hires you to answer the following questions: a) If they surveyed only 20 customers, how likely would it be that the average income of the sample would be within $500 of the actual average income among the population (which they now know to be 50,000)? (3 points) b) If they surveyed 50 customers, how likely would it be that the average income of the sample would be within $500 of the actual average income among the population? (3 points) c) Explain the difference between your answers to a) and b). (3 points) d) The general manager asks you to suggest a suitable sample size. What does your answer depend on? (3 points)