A professor has recorded exam grades for 20 students in his class, but one of the grades is no longer readable. If the mean score on the exam was 81 and the mean of the 19 readable scores is 85 , what is the value of the unreadable score?

The value of the unreadable score is

nothing.

5

Step-by-step explanation:

To obtain the total score for all the 20 students, we multiply the average score by the number hence

Total score for all 20 is 81*20=1620

Similarly, for the 19 students, the sum of their total score equals the product of the average and number of students hence

Total score for 19 readable is 19*85=1615

The difference between these two total scores ie for 20 and 19 students equals to the value of unreadable score. Therefore,

Difference=1620-1615=5

Therefore, the value of unreadable score is 5