Cassie has test grades of 71, 78 and 83 on the first three tests in her
pre-algebra class. What are the possible scores she can make on the
fourth test in order to make at least a letter grade of B after the fourth
test? A letter grade B means an average of at least 80. Let x represent
the score on the fourth test.
In order to have at least an average of 80 after 4 tests, the sum of her scores must be at least 80 * 4 = 320 so we can write the following inequality:
