A major car dealership has several stores in a big city. The owner wants to determine if there is a difference in the proportion of SUVs that are sold at stores A and B. The owner gathers the sales records for each store from the
past year. A random sample of 55 receipts from store A shows that 30 of the sales were for SUVs. Another random
sample of 60 receipts from store B shows that 42 of the sales were for SUVs. Assuming conditions for inference
are met, what is the 99% confidence interval for the difference in proportions of sales that are SUVs?
Find the z-table here.
(0.45 – 0.30)+1.96
0.45(1 -0.45) 0.30(1 -0.30)
60
55
+
(0.55-0.70) +1.96
0.55(1 - 0.55) 0.70(1 -0.70)
55
60
+
(0.45-0.30) £2.58)
0.45(1 -0.45), 0.30(1 -0.30)
60
55
+
0.55(1 -0.55) 0.70(1 -0.70)
0 (0.55-0.70) 2.58/
55
+
60