Correct Option
The average score for the first 3 tests is N points. Therefore, the total score for these 3 tests is 3N points.
On the fourth test, the student scored N + 20 points, as this exceeds the previous average score by 20 points.
The total score for all 4 tests is the sum of the scores from the first 3 tests and the fourth test: 3N + (N + 20) = 4N + 20.
To find the average score for the first 4 tests, divide the total score by the number of tests (4):
Average score = (4N + 20) / 4 = N + 5.
Incorrect Options
Options 1 (N + 20), 2 (N + 10), and 3 (N + 4) are incorrect because they do not accurately represent the calculation for the new average. The average is calculated by summing all scores and dividing by the total number of tests. Simply adding the excess score (20) to the previous average, or dividing it by an incorrect factor, does not yield the correct result. The correct method involves summing the total points for all tests and then dividing by the total number of tests, which leads to N + 5.