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).
Divide both sides by -4.
Therefore, the number of children is 5.