Girls = 9 units, boys = 8 units. There are 99 more girls, which is the 1-unit difference.<br><br>[[model:questions/solutions/q4498.png]]<br><br>• Difference → 9 units − 8 units = 1 unit → 99<br>• Total → 9 + 8 = 17 units = 17 × 99 = 1683<br><br>There are 1683 pupils in the school.<br>Check: girls 891, boys 792; 891 − 792 = 99; 891 + 792 = 1683. ✓