The whole is 100%. He gave 40% to his brother, leaving 60%. He sold half of that 60% (= 30%), so the 18 cards left are the last 30%.<br><br>[[model:questions/solutions/q5474.png]]<br><br>• Remaining after brother → 100% − 40% = 60%<br>• Sold → $$\frac{1}{2}$$ of 60% = 30%<br>• Left → 60% − 30% = 30% → 18 cards<br>• 10% → 18 ÷ 3 = 6<br>• 100% → 10 × 6 = 60<br><br>He had 60 cards at first.<br>Check: brother 24 + sold 18 + left 18 = 60. ✓