It’s the last day of school, ’round these parts, but as we know learning never really stops.

Case in point, the NBA this week announced that the league would be “using winning percentage” to determine who would qualify for this year’s playoffs.

What the heck was it using before?

The NBA was founded in 1946, and though the exact playoff format has changed through the years it has always followed one pretty basic principle: the teams are ranked based on their wins and losses.

When teams all play the exact same number of games, yes, it is easier to see who has a better record. A team that wins 50 out of 82 games has a higher percentage of wins than a team that wins 49 out of 82. But what if the team that had won 49 only played 80 games? What then?

The thing you see every day labeled “Pct.” in the standings will give you an answer. This is “winning percentage,” all though I’ve always enjoyed pointing out that when it’s carried out to its standard three decimal places you’re no longer looking at a percentage (which is out of 100) but a fraction of 1,000. (You never hear that Ted Williams was the last 40 percent hitter.) In our above case, 49 of 80 is 0.613 (rounded to the nearest thousandth) and 50 of 82 is 0.610 (also rounded). Better record? Forty-nine out of 80. (Think of it this way–the team that went 50 for 82 went 49 out of 80, then went one out of two. One for two is only 50%, a “worse” percentage.)

With the coronavirus interruption to the 2019-20 season, teams have played and will end up playing differing numbers of games.

Time to break out the calculators!

See, you love doing math in the summer.