Use the top-level ratio 3:2 to find how many boys and girls there are, then break each group down using sub-ratios.
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• Top-level ratio 3:2 means 5 units in total.
• 120 ÷ 5 = 24 per unit.
• Boys: 3 × 24 = 72
• Girls: 2 × 24 = 48
For the boys (sub-ratio 1 + 5):
• 6 parts = 12 per part
• those who wear glasses: 1 × 12 = 12
• don't: 5 × 12 = 60
For the girls (sub-ratio 1 + 3):
• 4 parts = 12 per part
• those who wear glasses: 1 × 12 = 12
• don't: 3 × 12 = 36
Total those who wear glasses: 12 + 12 = 24.
Check: 72 + 48 = 120 = total (120). ✓
Final Answer: 24