|When you add or delete rows or columns from a range, Excel updates the formula to reflect those changes.|
Try giving the range a Name and then using that Range Name in the formula as opposed to using the cell references.
Look up Range Names in Excel Help (or Google it) if you need instructions on how to create and use named ranges.
If the name range might expand or contract, you can use names that automatically update themselves to reflect those changes.
Read this for info on Dynamic Range Names.
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