Total collection = $3000
Total tickets = 720 (Adult's = $5, Child's = $3)
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Assumed all 720 tickets are child's tickets
720 x 3 = $2160
Difference in amount collected = $3000 - $2160 = $840
Difference in adult's and child's ticket = $5 - $3 = $2
Number of adult's tickets = $840 ÷ $2 = 420
Number of child's tickets =720 - 420 = 300
Answer: There are 300 child's tickets and 420 adult's tickets.
Check: 300 x $3 + 420 x $5 = $3000 (✓ correct)