Use the top-level ratio 7:2 to find how many adults and children there are, then break each group down using sub-ratios.
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• Top-level ratio 7:2 means 9 units in total.
• 90 ÷ 9 = 10 per unit.
• Adults: 7 × 10 = 70
• Children: 2 × 10 = 20
For the adults (sub-ratio 5 + 2):
• 7 parts = 10 per part
• order drinks: 5 × 10 = 50
• don't: 2 × 10 = 20
For the children (sub-ratio 1 + 1):
• 2 parts = 10 per part
• order drinks: 1 × 10 = 10
• don't: 1 × 10 = 10
Total order drinks: 50 + 10 = 60.
Check: 70 + 20 = 90 = total (90). ✓
Final Answer: 60