SUMIF is used to evaluate a range of input cells and conditionally add
corresponding values. You just need a simple IF:
=if((D10+D11-D13)0,(D10+D11-D13)*$A10,0)

"Kim" wrote:

Hi. I'm new to this formula stuff so please answer so that I can understand.
I thought I'd copied the format correctly (from Microsaft SUMIF Help) but I
keep getting an error message that something is wrong. I can't see what
though... The Function button seems to show that everything is correct.
=SUMIF(D10+D11-D13,"0",(D10+D11-D13)*$A10)

It's to display a percentage (A10) of a sum if the sum is 0.
If it's <=0 then no sum is needed. Or, in fact, I'd rather display '0' in
the cell. How would I do that?
Thanks.