official gamefiles rule from
http://richard_wilding.tripod.com/monorules.htm
PAYING RENT
When you land on a property that is owned by another player, the owner collects rent from you in accordance with the list printed on its Title Deed card.
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If the property is mortgaged, no rent can be collected. When a property is mortgaged, its Title Deed card is placed face down in front of the owner.
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It is an advantage to hold all the Title Deed cards in a color-group (i.e., Boardwalk and Park Place, or Connecticut, Vermont and Oriental Avenues) because the owner may then charge double rent for unimproved properties in that colour-group. This rule applies to unmortgaged properties even if another property in that colour-group is mortgaged.
It is even more advantageous to have houses or hotels on properties because rents are much higher than for unimproved properties. The owner may not collect the rent if they fail to ask for it before the second player following throws the dice.
. END OF GAME. The first player to go bankrupt retires from play, as in the regular game. However, when the second bankruptcy occurs, the game ends. Play immediately ceases, with the bankrupt player\'s turning over to there creditor all that they have of value, including buildings and any other properties.
This happens whether the creditor is a rival player or the Bank.
Each remaining player then values his/her property.
(1) Cash on hand
(2) Lots, Utilities and Railroads owned, at the price printed on the board.
(3) Any mortgaged property owned, at one-half the price printed on the board.
(4) Houses, valued at purchase price.
(5) Hotels, valued at purchase price including the value of the
three houses turned in.
THE RICHEST PLAYER WINS!