Is あたり used only to enumerate items?

Question

I usually read that あたり is used to enumerate things like A あたり, B あたり.

But lately I can also hear ひとつひとつあたり also used. Is this the same word?

How do you use the あたり in general? A search on a dictionary does not help that much.

当たり / あたり : n-adv n 1）hit 2）success 3）reaching the mark 4）per .. 5）vicinity 6）neighborhood P

Answer 1

あたり is used in a "per" or "for each" construct. Examples:

My car gets 30 km per liter.
私の車の燃費は１リットルあたり３０キロメートルです。

Today, the Japanese/American exchange rate is 79 yen per dollar.
今日、日米の為替レートは１ドルあたり７９円です。

Notice that the denominator goes first (before "あたり"), the precise opposite of English where the denominator goes after "per".

It is used for quantities (real numbers) as well as items (integers). So it is perfectly valid to use it when referring to quantities (as I did in the 燃費 example).