Taking away from stock in excel 2007

[Rich]

Ok so basically, i am using excel for stock purposes.
I insert the customers information, what product is being bought etc.. then
i want it to take away from the stock i have.
For example

Say i am selling Microsoft excel 2007 (Ironic isn't it?)
I would need it to recognise the products used in shipping.. (a4 envolope,
1st class stamp)

Say i have the column 'A', if i enter Microsoft Excel 2007 into there (From
a dropdown list)
and then the envolope quantity in 'B5' and stamps 'B6'

Is there any way how i can take away the envolope quantity and stamps
quantity by 1 when i enter 'Microsoft Excel 2007' into the column A

Thanks for your help

 

[Max]

Essentially you're looking for a 2 variable lookup ..
Suppose you have this kind of reference table in sheet: x, in A1:C3
Item1 Item2
Consum1 1 2
Consum2 3 4

And in another sheet,
you have the 2 variables (Item-Consumable) as lookup inputs -- these can be
from DVs -- in say:
A2: Item2
A3: Consum2
A4: Consum1
Then in B3, copied down:
=IF($A3="","",INDEX(x!$B$2:$C$3,MATCH($A$2,x!$B$1:$C$1,0),MATCH($A3,x!$A$2:$A$3,0)))
will return the intersection values from the reference table for
Item2-Consum2, Item2-Consum1, etc. Modify to suit. Useful? hit YES below