At the city museum, child admission is $6.10 and adult admission is $9.30. On Sunday, four times as many adult tickets as child tickets were sold, for a total sales of $909.30. How many child tickets were sold that day?

21 child tickets

Step-by-step explanation:

For this problem, you'd use a system of equations.

First, define your variables.

x = # of child tickets sold

y = # of adult tickets sold

There were 4 times as many adult tickets (y) as child tickets (x) sold, so:

4 x = y

4 x - y = 0

93 (4 x - y = 0)

372 x - 93 y = 0

The total revenue was $909.30, adult tickets were $9.30 each, child tickets were $6.10 each, so:

6.10 x + 9.30 y = 909.30

10 (6.10 x + 9.30 y = 909.30)

61 x + 93 y = 9093

372 x - 93 y = 0

433 x = 9093

433 x / 433 = 9093 / 433

x = 21