JM Property, a Nordic property developer, is considering the price for three housing subdivisions (apartment, single storey, and double storey) in Malmö, Sweden. Random samples of prices were taken for the three different types of houses by using the stratified random sampling method and determined the following statistical results.

Apartment Single Storey Double Storey Ni 520 875 605 ni 173 201 126 xi (in $000) 429 621 958 si 1.2 0.86 1.15

a. Using an unbiased estimation procedure, find the average selling price for the three different types of houses in Malmö.

b. Find a 95% confidence interval for the total selling price for the three housing subdivisions in Malmö.