historically, a part's length has been normally distributed with a mean of 4.5 inches and a standard deviation of 0.12 inches. suppose that we take samples of size 48 parts and find the sample mean of the length of the parts in the sample. what is the expected value of the sample mean? (another way to think of this is that we repeat the sampling many, many times with the same sample size and each time we compute the sample average of the weight. then we average all of those sample averages. what would the result be?)