Answer:
81 adult tickets
Step-by-step explanation:
Step 1:
Set up a system of equations
Since the adult tickets and student tickets add to 243, we can do
![a+s=243](https://tex.z-dn.net/?f=a%2Bs%3D243)
and the student tickets sold were 2x the adult tickets, we can do
![s=2a](https://tex.z-dn.net/?f=s%3D2a)
We can replace s in the first equation adding to 243 with 2a
![a+s(2a)=243\\3a=243\\](https://tex.z-dn.net/?f=a%2Bs%282a%29%3D243%5C%5C3a%3D243%5C%5C)
Step 2:
Solve for a. We can divide both sides by 3.
![a=81](https://tex.z-dn.net/?f=a%3D81)
Therefore, there were 81 adult tickets sold.
Step 3:
We can check our work! Since we learned earlier the student tickets are 2x adult tickets, we can multiply 81 by 2 and add that to 81 to see if it equals 243!
![s=2a\\s=2(81)\\s=162](https://tex.z-dn.net/?f=s%3D2a%5C%5Cs%3D2%2881%29%5C%5Cs%3D162)
And...
![162+81=243](https://tex.z-dn.net/?f=162%2B81%3D243)
So, 81 must be the answer!