Fixed total value vs changeables sub-values

[Alex126]

Hello. We have a question. I'll explain by the simple example. This is for the architectural purposes.
We have the corridor area - 30 units, (A1), the apartments' area-70 un.,(A2) and the total area - 100 un., (A3). We need to "play" with the apartments' and the corridor areas and to preserve the same value of the total area. Let's say, I put 10 units per corridor and it changes the value of apartments' area to 90 units to preserve 100 units totally. How to use the SUM function or another in this case. Thank you.

[RChad]

Please provide sample workbook

[RChad]

You can change the number of Apartments to get the number of Corridors but not both at same time.

See attached