is it posibble to adjust this formula to sum only numbers that are lower than 100? Like sum every fifth cell but only if in this cell is number lower than 100.
Welcome to Chandoo.org forums. You can add a condition (Blue colored portion) like below:
=SUMPRODUCT(P4:BFQ4;--(MOD(COLUMN(P4:BFQ4);5)=3);--(P4:BFQ4<100))