A common strategy when comparison shopping is to use the unit prices that are often available on the shelf to help consumers. This is a pretty solid strategy…except, apparently, at reader MZ’s local Target, where the retailer doesn’t feel the need to make sure that their unit pricing reflects reality at all.

He captured this image of the whole shelf of contact lens solutions at the store, then explained why it’s actually a better deal to buy the single 10-ounce bottle of Opti-Free solution than to buy in bulk and get two 10-ounce bottles.

“The single 10 oz. bottle of Alcon Opti-Free contact solution costs $8.99, while the twin pack, with 20 oz. total, costs $18.99–$1 more than two single bottles,” he points out. If you break down the math, things get more confusing. The shelf tag measures the price per pint for some reason, and a pint is sixteen ounces.

Yet if you divide $18.99 by 20 for the per-ounce price and then multiply it by 16 again, you get $15.19 per pint.

MZ notes that he submitted this issue to his local government, but hasn’t heard back. Just remember: while it’s helpful to use unit prices when you shop, they’re only useful when the retailer bothers to print up accurate signs.

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