In a certain large suburban housing development, all the houses were built at approximately the same time, with the same size and initial cost of construction. The median resale price of houses in the development has been established, but a real-estate agent wants to determine if multiple ownership affects the resale price of a house. From records at the county courthouse, she obtains a sample of the resale prices of 25 houses which have had more than one owner. In the sample, 15 were sold below the median price for houses in the area and 10 were sold above the median price.

a. Give the null and alternative hypotheses.

b. What is the value of P?

c. What conclusion should the agent make about the effect of multiple ownership on the resale value of a house in the area?

d. What factors could affect the validity of the conclusion?