Summing every second field in a row

Hey,

I have a problem. I'm supposed to sum values in every second field in a row(and the length of columns that have to be summed varies).

So basicly I have to SUM(J4,L4,N4,P4.....) and SUM(K4,M4,O4.....) for a variable number of columns.

Any help?

Thanks. I am very new to excel, so need some more help. The formula could probably work, but how can I set the "rng"? Will that automaticly be the whole range, or do I need to set it somehow?

=SUMPRODUCT(MOD(COLUMN(rng);2)*rng)

Thanks! That worked I actually tried to set the range that way, but I had something wrong.

Great