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Question: My husband and I are divorced (no kids), but we’ve been unable to sell our house, so we’re both still living in it. Since I’m away a lot on business, shouldn’t he be paying more than half of the utility bills?

Answer: But what if you take longer showers?

We’re not kidding. There are countless ways you and your ex consume water and energy unequally. Perhaps one of you likes to crank up the air conditioning or to grow tomatoes or to stay up late microwaving popcorn and watching movies. You can’t pick just one variable in the utility bill equation and then cry foul.

Moreover, life is filled with per person, as opposed to per usage, fees. Planes, trains and buses, for example, charge per seat, not per pound, even though heavyweights cost more to transport than bantams. Rare is the car wash that has more than two price points, even though autos come in all shapes and sizes. And, as you’ll discover once you sell the house and start looking for new digs, rarer still are roommates who are willing to split the utility bill on anything other than a per person basis.

Questions? Email Money Magazine’s ethicists – authors of “Isn’t It Their Turn to Pick Up the Check?” (Free Press) – at FlemingandSchwarz@right-thing.net.