Answer: 20 child tickets were sold that day.
Step-by-step explanation:
Let x represent the number of child tickets that were sold that day.
Let y represent the number of adult tickets that were sold that day.
On Sunday, twice as many adult tickets as child tickets were sold. It means that
y = 2x
At the city museum, child admission is $6.30 and adult admission is $9.60. The total sales for that day was $510.00. It means that
6.3x + 9.6y = 510- - - - - - - - - - - -1
Substituting y = 2x into equation 1, it becomes
6.3x + 9.6 × 2x = 510
6.3x + 19.2x = 510
25.5x = 510
x = 510/25.5
x = 20
y = 2x = 2 × 20
y = 40
