A major retail clothing store is interested in estimating the difference in mean monthly purchases by customers who use the store's in-house credit card versus using a Visa, Mastercard, or one of the other major credit cards. To do this, it has randomly selected a sample of customers who have made one or more purchases with each of the types of credit cards. The following represents the results of the sampling:
|
In-House Credit Card |
National Credit Card |
| Sample Size: |
86 |
113 |
| Mean Monthly Purchases: |
$45.67 |
$39.87 |
| Standard Deviation: |
$10.90 |
$12.47 |
Suppose that the managers wished to test whether there is a statistical difference in the mean monthly purchases by customers using the two types of credit cards, using a significance level of .05, what is the value of the test statistic assuming the standard deviations are known?
z = 11.91
z = 2.86
t = 3.49
z = 3.49