The three numbers add up to 3 × their average. Take out the two numbers (2 × their average) to leave the third.<br><br>[[model:questions/solutions/q4680.png]]<br><br>• Total of 3 → 3 × 16 = 48<br>• Total of 2 → 2 × 15 = 30<br>• Third number → 48 − 30 = 18<br><br>The third number is 18.<br>Check: (30 + 18) ÷ 3 = 48 ÷ 3 = 16. ✓