A divisive math problem has gone viral because netizens simply cannot agree on the correct answer. The equation hails from the 1950s and is baffling many people for a fascinating reason: it appears that over the years, the “rules” for how to solve it have changed.

9 - 9 ÷ 9 + 9 - 9 ÷ 9 = ?Can you work it out? Give it a try, and once you think you have the right answer, scroll down to see what all the controversy is about and what the correct answer is.

(9 - 9) ÷ 9 + 9 - 9 ÷ 9 = ? (0 ÷ 9) + 9 - 9 ÷ 9 = ? (0 + 9) - 9 ÷ 9 = ? (9 - 9) ÷ 9 = ? 0 ÷ 9 = 0The correct answer according to numerous others, however, is not 0 but 16.

If netizens’ comments are anything to go by, then mathematical methodology may have been taught differently in the 1950s. In order that everyone might achieve the same answer when tackling this equation, therefore, it is imperative that everyone uses the same rules. To this end, we the math community has employed a standardized set of rules known as the “order of operations.”

P: First, calculate the value of expressions inside parentheses (or brackets) E: Next, calculate any exponents M/D: Next, carry out any multiplications and divisions, working from left to right A/S: Finally, carry out any additions and subtractions, working from left to right

9 - (9 ÷ 9) + 9 - (9 ÷ 9) = ? 9 - (1) + 9 - (1) = ?Then we move on to solve addition and subtraction from left to right as follows:

(9 - 1) + 9 - 1 = ? (8 + 9) - 1 = ? 17 - 1 = 16Is this the same answer that you arrived at? If so, congratulations! Not everyone is able to solve it.

Anyone tackling these math puzzles using mental arithmetic or an “old-school” calculator may end up with a completely different result. In a mathematically ideal world, of course, everyone would be using the order of operations and homogeneity of results would be guaranteed.

“Well I did it wrong the first time,” another admitted. “I forgot you do the multiplication and division first. Thanks for the reminder, I guess I just don’t get to use that knowledge much on a daily basis.”

“We (of a certain age) were not taught BODMAS / BIDMAS / PEMDAS / UDAS / order of operations,” one Facebook user contributed, “we were taught left to right, that is all, giving 0 as [the] answer.”

“I am 62 years old and taught for 38 years,” another replied, adding a new perspective to the conversation. “Order of operations has been around all of that time.”

“You might have been taught different initials to remember what to do,” they continued. “However, the answer will always be 16. No matter what. You can’t have two different answers to [a] math problem.”

Until we achieve this consensus, however, cognitive conundrums such as these continue to go viral, entertaining netizens around the world.