Kim got 82% , 75% , and %74 on the first 3 test.
What grade does she need on the 4th test to have an average of 80% on all 4 test?
Let x be the grade Kim needs on the 4th test.
To have an average of 80% on all 4 tests, the sum of her grades on all 4 tests must be 80 x 4 = 320.
The sum of her grades on the first 3 tests is 82 + 75 + 74 = 231.
Thus, the grade she needs on the 4th test is:
x = 320 - 231 = 89.
Therefore, Kim needs a grade of 89% on the 4th test to have an average of 80% on all 4 tests.