Given:
Admission to the local movie theater is $3 for each child and $7 for each adult.
A group of 12 people pay $64 admission.
To find:
The number of children in a group.
Solution:
Let the number of children be x and number of adults be y.
According to the question,
Total persons :
...(i)
Total cost :
...(ii)
Multiply equation (i) by 7 and subtract the result from (ii).


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Divide both sides by -4.

Therefore, the number of children is 5.