How do I add a series of cells?

[readystate]

I have a spreadsheet with a series of drop down boxes with multiple values.
Is it possible to set up a formula that will add only those cells adjacent to
certain values? As an example, if the drop down has options such as PENDING
and CLOSED but I want to have the system automatically add only the dollar
amounts next to PENDING. Then, when it changes to CLOSED, I would like the
system to automatically re-calculate and shift the specific amount from
PENDING to CLOSED, can that be done? If so, how?

Any assistance will be greatly appreciated. Thanks.

J-P

[Dav]

If values are in a2:a100 and pending etc in cells b2:b100 and the reference at the top is in cell c1

sumif(b2:b100,c1,a2:a100)

regards

Dav