Amaya's overall grade will be an average of all the scores. To find the average, we must add up the scores and divide by the number of tests.
We know 2 of the scores, so we can represent the average as:
(48+61+x)/3
Now write the inequality.
60 <= (109 + x)/3 <= 69
Now let's find the lower bound to receive a D. First we need to multiply both sides by 3.
180 <= 109+x
Now subtract 109.
71 <= x
Now let's find the upper bound. Do the same thing but with the 69.
109+x <= 207
x <= 98
So Amaya will receive an overall grade of a D if she scores anywhere from 71 to 98 on the test.
