Split the 40 marbles into 10 equal parts (each = 10% = 4 marbles). He gave away 60% = 6 parts, so 40% = 4 parts are left.<br><br>[[model:questions/solutions/q4808.png]]<br><br>• 100% → 40, so 10% → 40 ÷ 10 = 4 marbles<br>• Left → 100% − 60% = 40% = 4 parts<br>• 40% → 4 × 4 = 16<br><br>Johnston had 16 marbles left.<br>Check: gave 60% × 40 = 24; 40 − 24 = 16. ✓