Seventy concert tickets were sold for $550. each adult ticket cost $9 and each children's ticket cost $5. find the number of adult tickets and the number of children's tickets sold.

Total tickets = 70
Total cost = $550

Adult's ticket = $9
Child's ticket = $5
Difference = 9 - 5 = $4

Assume all 70 are child's tickets
5 x 70 = 350

But the total cost was 550
550 - 350 = $200
The $200 must have come from Adult's tickets, which has a difference of $4.

200 ÷ 4 = 50
So there are 50 adult's tickets.

70 - 50 = 20
And there are 20 child's tickets.