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.

If you want to know for sure, try your hand at this basic math problem. It's harder than it looks — even if you think you have a solid grasp of good old PEMDAS.