I ended up writing a long post, hoping it can be just quoted to at least try to stop the same ol' cycle from starting over and over again.
The equation source of this discussion is 48÷2(9+3) = ????.
Most people able to solve basic first degree equations come up with two different solutions: 288 and 2. Why two and not one? Because the equation is written ambiguously.
The (9+3) can, in fact, be seen either as a number multiplied by the result of 48÷2, or as part of the denominator, together with the 2, the number 48 is divided by. So:
- The ones coming up with 288 see it as:
48
-- * (9+3)
2
- The ones coming up with 2 see it as:
48
------
2(9+3)
Why both camps are correct:
- The ones coming up with 288 are applying basic math rules, and considering the division sign as a simple division between the two numbers around it. Nothing strange, and nothing worth explaining. It's simply correct.
- The ones coming up with 2 are applying a type of notation commonly used in calculus, physics and chemistry where 1/xy is used to represent on a single line the fraction
1
--
xy
and not (1/x) multiplied by y. In this notation, y is also part of the denominator.
This notation is commonly used with implicit products, and usually with short expressions. Whether or not this is a consequence of implicit products by juxtaposition appearing as prioritary, at least visually since the elements are portrayed as "bound" together, compared to regular multiplications and divisions making the elements appear as more separate, is not really relevant. Fact is it's a real convention and it's commonly used in several textbooks and slides.
Proof: just do a Google search for "1/2