Question

The average total dollar purchase at a convenience store is less than that at a supermarket. Despite smaller-ticket purchases, convenience stores can still be profitable because of the size of operation, volume of business, and the markup. A researcher is interested in estimating the average purchase amount for convenience stores in suburban Long Island. To do so, she randomly sampled 24 purchases from several convenience stores in suburban Long Island and tabulated the amounts to the nearest dollar. Use the following data to construct a 90% confidence interval for the population average amount of purchases. Assume that the population standard deviation is 3.23 and the population is normally distributed.

$2	$11	$8	$7	$9	$3
5	4	2	1	10	8
14	7	6	3	7	2
4	1	3	6	8	4

(Round the answers to 3 decimal places.)

(blank) ≤ μ ≤ (blank)

Answer 1

Since population standard deviation is known, Use z-distribution.

2	11	8	7	9	3
5	4	2	1	10	8
14	7	6	3	7	2
4	1	3	6	8	4

Refer Standard normal table/Z-table or use excel function "=NORM.S.INV((1-0.05))" to find the Z-value.