Kelly's scores on the first three tests in her physics class are 79, 84, and 68. Determine all scores on the fourth test that will yield an average test score of at least 80.
(x + 79 + 84 + 68)/4 = 80
(x + 231)/4 =80
x +231 = 320
x + 231- 231 = 320-231
x = 89
Fourth test 89
To determine the scores on the fourth test that will yield an average test score of at least 80, we need to use the formula for average:
Average = (Sum of scores) / (Number of scores)
In this case, the average needs to be at least 80, so we have:
80 ≤ (79 + 84 + 68 + Fourth Test Score) / 4
Now we'll solve the equation to find the minimum score needed on the fourth test.
First, multiply both sides of the equation by 4 to get rid of the fraction:
320 ≤ 79 + 84 + 68 + Fourth Test Score
Next, combine the numbers on the right side of the equation:
320 ≤ 231 + Fourth Test Score
Subtract 231 from both sides of the equation:
320 - 231 ≤ 231 + Fourth Test Score - 231
89 ≤ Fourth Test Score
Therefore, any score on the fourth test that is equal to or greater than 89 will yield an average test score of at least 80.