Remark
The trick to this question is to find out what the total score is (85*25) then find out what the 9 scored as a total and what the 6 scored for their total. Findally subtract the two last numbers you got from the first number and divide by 10 (why ten?)
Step One
Find the total score of the 25 students.
Total = 25 * 85 = 2125
Step Two and Three
Find the totals for the 9 students and the 6 students.
The 9 students scored 100 so their total is
9*100 = 900
The 6 students scored 60 Their total is
60 * 6 = 360
The total of these 2 groups is 900 + 360 = 1260
Step Four
Find the total score for the remaining 10 students.
The total score for everyone = 2125
The total score for the 15 students = 1260
The total score of the ten remaining students = 865
Step 5
Find their average
865 / 10 = 86.5 <<<<<< Answer
