Change conditional format (color) of a cell based on another celll (Excel 2010)

you need two conditions, the first one is the one you have, which i am guessing looks something like this
=IF($B1>20,"TRUE","FALSE") and copied down for all of the cells that you are looking at.

Then you need to check the box next to that condition that says stop if true

Then create a new condition that says this
=IF($C1="X","TRUE","FALSE") and you can copy the conditional formatting to all cells that you need it on

Here is a sample spreadsheet that i have created for you, i have the formatting going down to B20 but you can do whatever you want in the manage formatting menu.

@ffnptown just a reminder.

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