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A fake Facebook event disguised as a math problem has been one of its top posts for 6 months
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I'm sure we're all geniuses here, but just in case...
Please excuse my dear aunt Sally.
Parenthesis, exponents, multiplication, division, addition, subtraction.
Why? Because a bunch of dead Greeks say so!
3x3-3÷3+3
(3x3)-(3÷3)+3
9-1+3
8+3
11
Not a genius. But if subtraction is last, why isn't it 9-4?
Addition/subtraction work out the same regardless of how you order the operations. If you do subtraction last you start with the original:
9-1+3
and you are adding 3 to the result of (9-1). Since you are trying to perform it before the (9-1) operation is carried out, you can add 3 to the 9:
12-1 = 11
or you can add three to the -1 and get:
9+2 = 11
You only end up with 9-4 if you were subtracting 3 rather than adding three. It all becomes more obvious if you read the original as:
9 + (-1) + 3