A student's grade in a course is the average of 4 test grades and a final exam that is worth twice as much as each test. Suppose a student has test grades of 91, 82, 83, and 92. 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.Then find the score they will need to receive on their final exam if they want to have a grade of 90 for the course.
As Jessica said, the equation for average is the sum of all the test scores divided by the number of tests. However, the question says that the final grade counts twice as much as each test. The final grade is the unknown, x, but it counts twice in the course average so we add 2x. Also, since it counts as 2 tests, we divide by 6.
So your equation would be:
(91 + 82 + 83 + 92 + 2x) / 6 = 90
(348 + 2x) / 6 = 90 Simplify
348 + 2x = 540 Multiply both sides by 6
2x = 192 Subtract 348 from both sides
x = 96 Divide both sides by 2
So the student will need to get a 96 on the final to get a 90 in the course.