In a class in which the final course grade depends entirely on the average of four equally weighted 100-point tests, Brad has scored 87, 89, and 78 on the first three. What range of scores on the fourth test will give Brad a C for the semester (an average between 70 and 79, inclusive)? Assume that all test scores have a non-negative value.

Step-by-step explanation:

Let x represent Brad's score on 4th test.

We have been given Brad has scored 87, 89, and 78 on the first three.

To find the range of Brad's test score, we will represent our given information in an inequality as:

Therefore, the range of score on the fourth test will be .

step-by-step explanation:

the triangles are similar. therefore the corresponding sides are in proportion:

              cross multiply

            divide both sides by 32