You are studying for final exam of the semester. Up to this point, you received 3 exam scores of 99%, 80%, and 70%. To receive a grade of B in the class, you must have an average exam score between 80% and 89% for all 4 exams including the final.

Find the widest range of scores that you can get on the final exam in order to receive a grade of B for the class. Use interval notation.

A.[68,69]
B.[63,100]
C.[71,100]

Question

You are studying for final exam of the semester. Up to this point, you received 3 exam scores of 99%, 80%, and 70%. To receive a grade of B in the class, you must have an average exam score between 80% and 89% for all 4 exams including the final. 

Find the widest range of scores that you can get on the final exam in order to receive a grade of B for the class. Use interval notation.

A.[68,69]
B.[63,100]
C.[71,100]

anonymous · Answer

The low end of the B range would be represented by:

.25x + .25(99) + .25(80) + .25(70) = 80

solving that gives you x = 71

The high end of the B range could be represented by:

.25x + .25(99) + .25(80) + .25(70) = 89

solving for x gives you x=107

107 is outside the range of things you could actually get on the exam

so to get a B in the class you must get in the interval of:

C.[71,100]