Charlie Brown is in the classroom looking at the blackboard which holds the sums, '7 + 6' and '4 - 3' He asks, "Why do I always get the hardest problems?"
He puts his finger to his mouth and says, "Let's see...if our team had seven and we scored a touchdown, but failed to convert, we'd have thirteen..."
He turns to the board and continues, "And if par on a hole is four, and you get a birdie, you're one under..."
He walks off smiling as the board now reads,'7+6=13' and '4-3=1'.