In early 2009, the economy was experiencing a recession. But how was the recession affecting the stock market? Shown are data from a sample of 15 companies. Shown for each company is the price per share of stock on January 1 and April 30 (The Wall Street Journal, May 1, 2009).

a. What is the change in the mean price per share of stock over the four-month period?
b. Provide a 90% confidence interval estimate of the change in the mean price per share of stock. Interpret the results.
c. What was the percentage change in the mean price per share of stock over the four-month period?
d. If this same percentage change were to occur for the next four months and again for the four months after that, what would be the mean price per share of stock at the end of the year2009?

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January 1 () April 30 ($) Applied Materials Bank of New Yorlk 3 Cisco Systems 5 Johnson & Johnson 1 Procter & Gamble