Monopoly Wiki

When none of the Utilities are purchased the rules are clear.   You can buy it from the bank once you advance to it.  If another player already has that card or has a monopoly I'm not sure how it works.  The Utility Card is specific you land on the spot you roll either and pay 4x or 10x depending if you have monopoly.  So when the Chance card is used on top of a Utilities Monopoly?  What do you pay?  For example:

I roll a 10 from two die:

Two utilities (monopoly) 10x10 = 100 with chance card 100x10 = 1000

OR is it just doubled?

Two utilities (monopoly) 10x10 = 100 with chance card 100+100 = 200

I got in a heated exchange with my wife and we almost got a divorce so a little clarification would be nice.  Who's right?