A batter scored 360 runs in 15 innings during a season and was not out in 3 of those innings. A batting average is defined as the runs scored divided by the number of COMPLETED innings, an innings ending not out being treated as incomplete. What is the batter's average?

The completed innings are 15 − 3 = 12, so the average is 360 ÷ 12 = 30 runs. The definition divides by dismissals rather than by appearances because a not-out score is a total that had not finished growing, and dividing by it would understate the batter. The value 24 = 360 ÷ 15 divides by every innings played, ignoring the definition given, and it is always the smaller figure — which is why the two must not be confused. The value 20 = 360 ÷ 18 adds the not-outs instead of subtracting them. The value 12 is the number of completed innings itself, that is the divisor quoted in place of the quotient.