Hello, I was looking at the solutions for the book "Business Analytics: Data Analysis & Decision Making by Cengage" specifically Chapter 9, Problem 70 .

This is the link of the solution (https://www.coursehero.com/textbook-solutions/Business-Analytics-Data-Analysis-Decision-Making-7th-Edition-9780357109953-631/Chapter-9-Problem-70-1073026/)

The problem states the following:

A cereal company wants to see which of two promotional strategies, supplying coupons in a local newspaper or including coupons in the cereal package itself, is more effective. (In the latter case, there is a label on the package indicating the presence of the coupon inside.) The company randomly chooses 80 Kroger's stores around the countryall of approximately the same size and overall sales volumeand promotes its cereal one way at 40 of these sites, and the other way at the other 40 sites. (All are at different geographical locations, so local newspaper ads for one of the sites should not affect sales at any other site.)

• Sales: number of boxes sold during the first week of the company's promotion
• Promotion Type: 1 if coupons are in local paper, 0 if coupons are inside box

a. Based on all 80 observations, calculate:

1. the difference in sample mean sales between stores running the two different promotional types
2. the standard error of this difference
3. a 90% confidence interval for the population mean difference

My only question is the reason why we should use a paired sample hypothesis test to solve this problem instead of a two sample hypothesis test.