The management of a supermarket wants to find if there is a relationship between the number of times a specific product is promoted on the intercom system in the store and the number of units of that product sold. To experiment, the management selected a product and promoted it on the intercom system for 7 days. The following table gives the number of times this product was promoted each day and the number of units sold.

a. With the number of promotions as an independent variable and the number of units sold as a dependent variable, what do you expect the sign of B in the regression line y = A + Bx + E will be?
b. Find the least squares regression line Å· = a + bx. Is the sign of b the same as you hypothesized for B in part a?
c. Give a brief interpretation of the values of a and b calculated in part b.
d. Compute r and r2 and explain what they mean.
e. Predict the number of units of this product sold on a day with 35 promotions.
f. Compute the standard deviation of errors.
g. Construct a 98% confidence interval for B.
h. Testing at a 1% significance level, can you conclude that B is positive?
i. Using α = .02, can you conclude that the correlation coefficient is different from zero?

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Number of Promotions per Day 15 Number of Units Sold per Day (hundreds) 42 30 18 12 38 30 26 17 15