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

Revise how to add, subtract, multiply and divide negative numbers using the correct order of operations (BIDMAS) and how to work this out on a calculator.

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.