Surely it does kind of make a little bit of difference about the order you do them in...
Consider...
8 - 4 + 2 = ?

You could group it as 8 - (4+2), which would give you 2. Or...

You could group it as (8-4) + 2, which gives you 6.

Basically, though, if you've written your sum as arse-about-face as that, you deserve to be given a wrong answer. You need to add some brackets...

Similarly,

8 / 4 * 2 grouped differently becomes either

8 / (4*2) = 1 or...
(8/4) * 2 = 4.

So... for the times when somebody has set up a very, VERY badly put together sum, it CAN actually matter (purely for convention) which order you do them in...

Would now (that I have bored you all shit-less) be a good time to admit that I used to be a little bit of a maths teacher?
(Serotonicity was a naughty boy on..., Tue 24 Jan 2012, 17:49, 1 reply)

I think the idea is they have equal precedence,
so you do them left to right.
( The Awful Puppy Bakery is still bored, Tue 24 Jan 2012, 18:17, closed)

Well I'm glad I was never a proper maths teacher then.

My rule was always if there was any chance of misinterpreting it, to put some brackets in, which seemed to work out fine.
(Serotonicity was a naughty boy on..., Tue 24 Jan 2012, 18:29, closed)

I've been brushing up my maths at the Khan Academy.
I'm going with what Sal says. He has three degrees and a masters from MIT.
( The Awful Puppy Bakery is still bored, Wed 25 Jan 2012, 1:35, closed)