A study was conducted to determine whether automobile repair charges are higher for female customers than for male customers. Twenty auto repair shops were randomly selected from the telephone book. Two cars of the same age, brand, and engine problem were used in the study. For each repair shop, the two cars were randomly assigned to a man and woman participant and then taken to the shop for an estimate of repair cost. The repair costs (in dollars) are given here.

a. Which procedure, t or Wilcoxon, is more appropriate in this situation? Why?
b. Are repair costs generally higher for female customers than for male customers? Use α = .05.

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Repair Shop Female customers 871 684 795 838 1,033 917 1,047 723 1,179 707 817 846 975 868 1323 79 1157 932 1,089 770 Male customers 792 765 511 520 618 447 548 720 899 788 927 657 851 702 918 528 884 702 839 878 1 2 3 4 5 6 7 8 9 10 1 12 13 14 15 17 18 19 20