Question 285789
OK you are dealing with averages the sum of a group of numbers divided by the AMOUNT of different numbers is an average or a 'mean'. So what do we have here?
Five test scores PLUS identical scores on three more  tests DIVIDED by the total of 8 tests in all equals an average of 90. Do the Math...
 438 plus 3x= 720
3x=282
x=94
so the scores would look like this: 83, 92, 78, 96, 89, 94, 94, 94   When you divide their sum by 8 you get the average score of 90.

The answer to problem is D.