=SUMPRODUCT(--(MOD(ROW(1:25),2)=1),TRANSPOSE(A1:Y1))-SUMPRODUCT(--(MOD(ROW(1:25),2)=0),TRANSPOSE(A1:Y1))
may i ask one out-of-topic question:
what is the function of "--" in excel formulas?
Regards... OP
I tried yours both. Richard's shows "$Value!"