Though people are usually taught that putting a number next to parentheses means multiply, what it actually means is the number is a FUNCTION OF what's in the parentheses... meaning that in the above scenario, two is a function of 1+2, meaning you apply the 2 to what's in the parentheses (1+2, or 3) giving you 6.
Meaning it's 6/6 = 1.
You can't really say it's (6/3) * (1+2), because that's extrapolating parentheses to indicate multiplication, when they really don't-- it's just an easier way of thinking of it (which in this case is inaccurate). That's why using PEMDAS or what have you doesn't work here, because there's no "M".
edit: to be a little more clear, let's say you have the function 6/f(x). Looking at it like that, most of you would probably agree that you can't separate f from x. Well, if f=2 and x=3, you STILL can't separate f from x, even if we've assigned it a constant.