=+4. Suppose that after computing xn based on n sample observations x1, . . . , xn, another observation xn11 becomes available. What is the relationship between the mean of the first n observations, the new observation, and the mean of all n11 observations?

The mean of the 10 observations in Exercise 1 is 640.5. If an 11th property had sold at a price of 780, what would be the mean sale price for all 11 properties?