I have a worksheet organized as:
WeekDay / WoodShop / Spa / Pool
Monday / / 1 / 4
Tuesday/ / 2 / 2
Wednesday/ / 1 / 4

I used the Data/Subtotal/Average functionality to determine the average
number of participants in each of the events over the period of time, and
the Woodshop average's cell displays "#DIV/0".

I understand that dividing 3 by 0 is an error, but I want Excel just to
leave the cell blank.

I've tried conditional formatting using the Is Formula / =iserror as
suggested in Help, but Excel is ignoring this.

Is there any way to make Excel do what I want?

TIA,