From the article: "More than half of the participants in the Yankelovich focus groups questioned the price of our burger." They "did research" which found that

From the article: "More than half of the participants in the Yankelovich focus groups questioned the price of our burger." They "did research" which found that a handful of people didn't understand fractions, in an unusual group social setting which can easily amplify oddball beliefs if other participants aren't 100% confident. You can do general polling of a question like this, which will give you actual serious data about whether Americans understand fractions.