24 child tickets were sold that day.
Step-by-step explanation
Lets assume, the number of child tickets sold is
![x](https://img.qammunity.org/2019/formulas/mathematics/college/lhtxftojjkzsmo3o2h4ilq8naohracejui.png)
As there are three times as many adult tickets as child tickets were sold, so the number of adult tickets will be
![3x](https://img.qammunity.org/2019/formulas/mathematics/middle-school/wm4h7tocuclckq7ujvxowo954795zqlhcq.png)
Cost of each child ticket is $6.20 and cost of each adult ticket is $9.80
So, the total cost of x child tickets = $ 6.20x
and the total cost of 3x adult tickets = $9.80× 3x = $29.40x
Total amount of sales is given as $854.40 , so the equation will be...
![6.20x+29.40x=854.40\\ \\ 35.60x=854.40\\ \\ x= (854.40)/(35.60)=24](https://img.qammunity.org/2019/formulas/mathematics/high-school/h9i5a2cpdsjer65s5rj8kwb5a3zcysa485.png)
So, 24 child tickets were sold that day.