Answer: The total number of tickets that John sold is 27
Explanation:
Let x represent the number of adult tickets that John sold at the concert.
Let y represent the number of children's tickets that John sold at the concert.
Adult tickets cost $6.50 and children's tickets cost $4.50. John collects a total of 157.50 from the ticket sales it means that
6.5x + 4.5y = 157.5 - - - - - - - - - -1
John sells twice as many adult tickets as children's tickets. This means that
x = 2y
Substituting x = 2y into equation 1, it becomes
6.5 × 2y + 4.5y = 157.5
13y + 4.5x = 157.5
17.5y = 157.5
y = 157.5/17.5 = 9
x = 2×9 = 18
The total number of tickets that John sold is 9 + 18 = 27