IFERROR help!

[therichterscale]

I have a cheat sheet for payment discounts for when parents pay tuition in full and or semi annual. Each discount carries a different value of which I have created a drop down list for (the same goes for the tuition amount). I'm trying to remove the value result with an iferror. If I don't have all 3 students filled, my total at C22 won't calculate appropriately because of the value. Below is the formula that I have inputted for C14 and C20. Where would I add the iferror?

=IF((OR(C17+C19-C18>0,C17+C19-C18<0)),C17+C19-C18," ")

 

[Joe4]

Note that when dealing with numbers that you want to add/sum, you should NEVER return text values.
A single space (" ") is a text value. Either return the empty string ("") or 0, i.e.

=IF((OR(C17+C19-C18>0,C17+C19-C18<0)),C17+C19-C18,"")

or

=IF((OR(C17+C19-C18>0,C17+C19-C18<0)),C17+C19-C18,0)

Also note that if you try to use a Text entries when adding using "+", you will get an error.
However, if you use the SUM function instead of "+", it will simply ignore text entries and not return any errors.