This week, a centuries-old geometric exercise that is easier than it looks, and a disputed division of a soft drink between a pair of twins.

Numbers don’t just mark superstition. They also define achievement. Malcolm Gladwell popularized the 10,000-hour rule as one key to becoming world-class at something — whether it’s violin, coding or ...

So you’re booking your flight, and just when you’re about to check out, the airline asks if you’d like to pay a little something to offset your share of the flight’s pollution.