575 adult tickets and 325 child tickets were sold.
adult tickets = a
child tickets = c
a + c = 900
2a + c = 1150
Subtract c from the equation on top to get a = 900 - c
Substitute this value into the second equation 2(900 - c) = 1150
Simplify to make 1800 - 2c = 1150
Add 2c to both sides
1800 = 1150 + 2c
Subtract 1150 from each side
2c = 650
Divide by 2 so that c = 325. Therefore, 325 child tickets were sold.
To find the number of adult tickets, subtract 325 from 900
The remaining number (a = 900 - 325 = 575) is how many adult tickets were sold. 575 adult tickets were sold.
