15.17 Smartphone sales A smartphone retailer wants to compare the sales of smartphones with and without offering a discount. She wanted to see if the sales increased or not. In an experimental study over 6 days, she offered a discount on 3 days while no discount was offered on the other 3 days. The final sales are in the table.

a. Find the ranks and the mean rank for sales with and without discount.

b. Show that there are 20 possible allocations of ranks for smartphone sales with and without discount.

c. Explain why the observed ranks for the two groups are one of the two most extreme ways the two groups can differ, for the 20 possible allocations of the ranks.

d. Explain why the P-value for the two-sided test equals 0.10.

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Sales with discount Sales without discount 21 25 23 11 13 14