A student’s course grade is determined by averaging 4 exams. The student’s grades on the first 3 exams are 85, 87, and 89. What does the student need to get on the 4th exam in order to get an A for the course (average of at least 90)? To get a B for the course (average of at least 80)?

a). At least 99 marks should be scored by the student to get an A.

b). Student has to score at least 59 and less than 99 grades in the 4th exam to get a B.

Step-by-step explanation:

Student's grades on the first three exams are 85, 87, and 89.

Since student's course grade is to be determined by averaging 4 exams.

So average of 4 exams =

Here x is the grade obtained by the student in 4th exam.

If the average of 4 exams to get an A is at least 90 so the expression will be

261 + x ≥ 360

x ≥ 360 - 261

x ≥ 99

At least 99 marks should be scored by the student to get an A.

To get a B (Average of at least 80) the expression will be

320-261 ≤ x < 360-261

59 ≤ x < 99

Therefore, student has to score at least 59 and less than 99 grades in the 4th exam to get a B.