Cut the 70 people into 10 equal units (each = 7). Adults take 3/10 = 3 units. The remainder is 7 units; 1/7 of it (1 unit) are boys, the other 6 units are girls.<br><br>[[model:questions/solutions/q4356.png]]<br><br>• 1 unit → 70 ÷ 10 = 7 people<br>• Adults → 3 units = 21; remainder = 7 units = 49<br>• Boys → 1/7 of 49 = 1 unit = 7<br>• Girls → 6 units = 6 × 7 = 42<br><br>There are 42 girls.<br>Check: 21 adults + 7 boys + 42 girls = 70. ✓