The average weight of a bar of soap should be 6.4 ounces with a standard deviation of 0.2 ounces. A sample of 20 bars of soap found the average to be 6.3 ounces with a standard deviation of 0.3 ounces. What is the test statistic for testing whether or not the mean exceeds 6.4 ounces

The testing statistic is - 2.237

Step-by-step explanation:

Test statistic (z) = (sample mean - population mean) : (population standard deviation/√n)

sample mean = 6.3 ounces

population mean = 6.4 ounces

population standard deviation = 0.2 ounces

n (sample size) = 20

z = (6.3 - 6.4) : (0.2/√20) = - 0.1 : 0.0447 = - 2.237