How much can you sell houses for in Monopoly and what factors determine the selling price of houses in the game?

In Monopoly, houses can be sold for half of their original purchase price. The selling price of houses in the game is determined by the number of houses already built on the property, as well as the property's color group. The more houses that are built on a property, the higher the selling price will be. Additionally, properties in the same color group can affect the selling price, as building houses on all properties in a color group increases the value of each individual property.