Amathematics professor lost a test paper belonging to one of her students. she remembered that the mean score for the class of 40 was 85 and that the sum of the 39 other scores was 3310. what was the grade on the paper she lost?

The mean score of class of 40 was 85.

Using the formula of mean, we can write:



This is the sum of scores of the entire class i.e.40 students. Professor also knows the sum of scores of remaining 39 students. If she subtracts the sum of scores of 39 students from the sum of scores of 40 students, she can find the test scores of her student.

So, the test score of her student = 3400 - 3310 = 90.

This means the grade on the paper she lost was 90 .