Answer: An adult ticket cost $12
A child ticket cost $5
Explanation:
Let x represent the price for one adult ticket.
Let y represent the price for one child ticket.
A movie theater sold 4 adult tickets and 7 children's tickets for $83 on Friday. It means that
4x + 7y = 83 - - - - - - - - - - - -1
The next day the theater sold 5 adult tickets and 6 children tickets for $90. It means that
5x + 6y = 90 - - - - - - - - - - - -2
Multiplying equation 1 by 5 and equation 2 by 4, it becomes
20x + 35y = 415
20x + 24y = 360
Subtracting, it becomes
11y = 55
y = 55/11 = 5
Substituting y = 5 into equation 1, it becomes
4x + 7 × 5 = 83
4x + 35 = 83
4x = 83 - 35 = 48
x = 48/4 = 12