[EmxATW5m]

And it's a damn simple equation too:
48 / 2 ( 9 + 3 )

Basic math rules say that you first calculate things within parenthesis (if there's more than one, you start from possible parenthesis inside another parenthesis etc), multiplying and dividing are equal and done in order from left to right.
Also since there's parenthesis next to number without anything between them, they're multiplied.

So the above equation goes like this:

48 / 2 ( 9 + 3 ) =
48 / 2 ( 12 ) =
24 ( 12 ) =
24 * 12 =
288

However, some calculators count it like this:

48 / 2 ( 9 + 3 ) =
48 / 2 ( 12 ) =
48 / 24 =
2

Strangely enough, some people are quite convinced the latter way should be correct, and not the former.

Here's wolfram alphas take on it:
http://www.wolframalpha.com/input/?i=48/2(9%2B3)

And examples where calculators fail or do it right: