Carol received an 82, 94, and 88 on three Social Studies tests.What did Carol receive on her fourth test if her average on all four tests was 85?
You can propose a simple equation, by knowing that the average is the sum of all the list of numbers divided by the number of numbers.
We define x as the score of the four test since we don't know it:
The left side is how you calculate the average and the right side is the result that you already know (85).
Solving for x: