The calculated value of the Z statistic to test the potential buyer's belief at the 1% significant level is -2.57512627.
The calculated Z score is slightly greater than the critical value of -2.575, the potential buyer's view that weekly store revenues are less than $7,000 stands vindicated.
Since store revenues are assumed to be normally distributed and population standard deviation is given, we can use the Z-test. The relevant test statistic is the Z-score.
We use the following formula for calculating the Z score:
Z = (X - μ) / (σ /√n)
Substituting the relevant values we get,
Z = (6400 -7000) / (1042/√20)
Z = -600 / 232.9982833
Z = -2.57512627