I know that 2 ounces is the correct answer, but I don't know how to solve the problem to get that solution.

Please provide a detailed explanation of how to solve this problem by hand and include any formulas used. Thanks!

A quality analyst wants to construct a sample mean chart for controlling a packaging process. He knows from past experience that whenever this process is in control, package weight is normally distributed with a mean of 20 ounces and a standard deviation of two ounces. Each day last week, he randomly selected four packages and weighed each What is the standard deviation of the sampling distribution of sample means for whenever this process is in control? 0.1 ounces 0.4 ounces 0.5 ounces 1 ounce 2 ounces