Failed = 25% = 1 unit; passed = 75% = 3 units. Passed has 2 units more than failed, and that gap is 16.<br><br>[[model:questions/solutions/q5446.png]]<br><br>• Passed − failed → 3 units − 1 unit = 2 units → 16<br>• 1 unit (failed) → 16 ÷ 2 = 8<br><br>8 pupils failed the test.<br>Check: passed 24 − failed 8 = 16. ✓