The two volumes add up to twice the average. The fuller bottle is 4 units; the other is 1 unit, so 5 units in all.<br><br>[[model:questions/solutions/q4673.png]]<br><br>• Total → 2 × 625 = 1250 ml<br>• 5 units → 1250 ml<br>• 1 unit (less) → 1250 ÷ 5 = 250 ml<br>• More → 4 × 250 = 1000 ml<br><br>The bottle with more water has 1000 ml and the bottle with less water has 250 ml.<br>Check: (1000 + 250) ÷ 2 = 625 ml and 1000 = 4 × 250. ✓