Hello all! :-)

I'm trying to make a very simple inventory system so that i can track
stationary as it is delivered, then distributed to the various departments at
my company. Exciting huh?
I can do the simple stuff ok, use vlookup's to get info on stock from
different sheets etc, but here comes the question.

I'm going to use the first sheet as a "form" to enter data in, eg: Item
number 1001, quantity 10. How do i then get the inventory quantity on another
sheet to add these 10 items to a number that is already in that cell.
eg: 25 in stock already, add the 10 new ones, new inventory quantity 35?

Have been trying a few ways but cannot make it work, am pretty good with
things like this normally, but have reached a dead end.

Thanks for any help.