how to calculate mean production for a period

J

John Smith

i have a table like this:


type date kg
0 18.03 400
1 18.03 200
0 20.03 500
1 20.03 100

this r all the quantities at the store

and the formula is like:
mean production for 18.03 - 20.03 = [(500-100) - (400-200)] / (20-18)

that is if type is '1' u subscribe

any ideas how it can be done with access queries?

TIA
 
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