The latest nationally representative adult literacy test administered by the U.S. Department of Education found that 10% of U.S. residents aged 16 to 65 years can correctly answer a question requiring knowledge of the fact that “mean” is another word for “average” and the ability to calculate a simple average. During this test, people were allowed to use calculators and take as much time as needed. You can see such a question at the link below. It is the one relating to restaurant expenditures.