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Ask Marilyn: Are You Always Getting Change?
Fran VanHoy of Menifee, California, writes:
Marilyn: My husband and I have an ongoing discussion about how frequently the total dollar amount in a grocery store will come out even. He says it's every one hundred times. I say that I've shopped for years, and the total bill has been even to the dollar only a few times. But maybe this is because I'm only one shopper in one market, so even though the total may be even every one hundred times for different shoppers in different markets, it won't necessarily happen to me. What do you think?
First, even if all the prices in the grocery store were random, and all the shoppers chose products randomly, the total bill would not be even to the dollar every one hundred times. Consider flipping a coin. If you flipped a coin 10,000 times, you would not expect half the flips to be heads and half tails. In fact, you would be shocked if this happened.
Second, the prices in the grocery store aren't random. They're full of 9-cent endings and seldom end with certain digits, etc. And shoppers don't choose products randomly. The only way to determine how frequently the total dollar amount is even would be to conduct a survey of many grocery stores' actual receipts.