Excel 2007 : Recognize Input in Col. A & Update Running Total of Col. B Values

So, I'm just finding me way through Excel and learning every minute. This one formula I haven't been able to figure out:

I am entering data for trucking into a spread sheet...the trucks are coming from three different locations P1, P2 and P3.
In my "A" column I enter any one of those three locations depending on the truck, in the same row, in the "B" column, I enter a weight for the truck.

Separately, I want to create (3) automatically updating total weights. One for P1 trucks, one for P2 and one for P3.

So it's a combination of two formulas really, it needs to recognize what is in the A column, and the corresponding value in the adjacent "B" cell.

Any ideas?

Have a look at the SUMIF function in Excel Help.

e.g.

=SUMIF($A$1:$A$10,"P1",$B$1:$B$10)

this will sum B1:B10 where corresponding cells in A1:A10 contain P1.

You can adjust the ranges to suit your data, and you can substitute "P1" with a cell reference containing P1 so that you can copy formula down...