Let's say the set of downs starts at the 20 yard line (maybe the kicking team kicked deep, the receiving team took a knee and so play starts at the 20).
Ok - we're at the 20. First down - they advance 5 yards. So we're now at the 25. We can write that mathematically as:
20 + 5= 25
So the second play they get sacked deep and lose 6 yards. So we subtract 6:
25 − 6=19
So what's the change in yardage for the 2 plays? We are on the 19 and started at the 20, so we can write:
19 − 20= −1
and this makes sense because we know we advanced 5 and fell back 6:
