This would seem to be a pretty simple calculation:

But many non-mathematicians stumble over it. The natural impulse is to start working from left to right:

– start with 9, subtract 3 to get 6

– divide 6 by 1/3 to get 18 (remember, dividing by a fraction is the same as multiplying by the reciprocal!)

– then add 1 to get 19.

If you got this, sorry, but it’s the wrong answer. Don’t feel too bad, since only 10% of viewers on Facebook got this problem right.

Working this way overlooks the fact that mathematics has a specific order of operations that takes precedence over the left-to-right approach. The mnemonic used is BODMAS: calculate functions in **B**rackets first, then do **O**rders (i.e. exponents and square roots), then **DM** for division and multiplication, and finally **AS** for addition and subtraction.

With this in mind, we can reconsider the equation. Since division and multiplication have to come first, we start by dividing 3 by 1/3 to get 9. Then do the addition and subtraction left to right: 9 – 9 yields 0, plus 1 for the correct final answer, 1.

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