The term variable is used in statistics to mean a number,
characteristic or quantity that changes with time or takes different values at
different situations. There are two basic types of variables namely independent
and dependent

You run a gizmo factory. Over the past year the average output of the factory is 480 gizmos and the standard deviation of that output is 10 units per day. In repeated random samples of size n = 40 days, the expected value of sample mean is: