Answer: 200 adult tickets and 400 student tickets were sold.
Explanation:
Let x represent the number of adult tickets that were sold.
Let y represent the number of student tickets that were sold.
Adult tickets to a play cost $1.75 each and student tickets cost $1.25 each. If the income from the play was $850, the expression would be
1.75x + 1.25y = 850- - - - - - - - - -1
Suppose there are twice as many student tickets sold as adult tickets. This is expressed as
y = 2x
Substituting y = 2x into equation 1, it becomes
1.75x + 1.25 × 2x = 850
1.75x + 2.5x = 850
4.25x = 850
x = 850/4.25
x = 200
y = 2x = 2 × 200
y = 400