One short math problem set the internet ablaze this weekend—and incited charged arguments on math teacher Twitter, too.

To help students in the United States remember this order of operations, teachers drill the acronym PEMDAS into them: parentheses, exponents, multiplication, division, addition, subtraction.

The confusion has to do with the difference between modern and historic interpretations of the order of operations. The correct answer today is 16. An answer of 1 would have been correct 100 years ...