The arithmetic mean of the scores of a group of students in a test was 40. The brightest 10% of them secured a mean score of 60 and the dullest 20% a mean score of 30. The mean score of remaining 70% is?
Select:
A) 25  B) 30  C) 40  D) 42  E) 48
Let the required mean score be x   10*60 + 20*30 + 70*x = 40*100   600+600+70x = 4000   x = 40   Answer is 40
<result>C</result>
The arithmetic mean of the scores of a group of students in a test was 40. The brightest 10% of them secured a mean score of 60 and the dullest 20% a mean score of 30. The mean score of remaining 70% is?