Spreadsheet problem

[purbeck]

Probably very simple to those who actually know how to use spreadsheets properly - I'm trying to do the following:

Select a range of cells that contain fixed numeric values.
Update all those values by a fixed percentage, defined in a given cell, so that the updated values appear in the original cells.

I don't want to add extra cells to hold the updated values - I know that this is the simple solution but for various reasons I must have the original values replaced in the original cells.

I assume I need to use some sort of macro to do it, but cannot actually see how to make this happen.

All advice, guidance or solutions gratefully received.

[purbeck]

Please ignore - posted in the wrong forum because it's late and I'm tired... now reposted in Calc.