A student's grade in a course is the average of 4 test grades and a final exam that is worth three times as much as each test. Suppose a student has test grades of 90, 88, 81, and 94. Write an equation to model this situation where x is the student's grade on the final exam and y is the student's average for the course.

AVG=(90+88+81+94+3x)/7

To model this situation, we need to consider the weightage of the test grades and the final exam.

Let's first calculate the average test grade. To find the average, we add up the test grades and divide it by the number of tests:

Average test grade = (90 + 88 + 81 + 94) / 4

Now, since the final exam is worth three times as much as each test grade, we can consider it as three additional test grades:

Total test grades = (90 + 88 + 81 + 94) + (x + x + x)

The total number of test grades is now 7.

To find the student's average for the course, we add up the total test grades and divide it by the total number of test grades:

y = (90 + 88 + 81 + 94 + 3x + 3x + 3x) / 7

Simplifying the equation, we have:

y = (353 + 9x) / 7

Therefore, the equation to model this situation is y = (353 + 9x) / 7.