OK, this will sum alternate columns ( even columns, as opposed to "odd" columns, so F, H, J & L ), and is an array formula ( entered using

**Ctrl-Shift-Enter** instead of Enter ):

Code:

`=SUM(IF(MOD(COLUMN(F5:M44),2)=0,F5:M44,0))`

When you press

**Ctrl-Shift-Enter** Excel will put curly brackets around your formula to indicate that it's an array formula.

As you can see, it is very easy to extend this formula to cover more columns, and can be switched to sum "odd" columns by changing the "=0" to be "=1". Remember to re-enter with

**Ctrl-Shift-Enter** when altering the formula.