The arithmetic mean of the scores of a group of students in a test was 52. The brightest 20% of them secured a mean score of 80 and the dullest 25%, a mean score of 31. The mean score of remaining 55% is :
Let the total number of people be 100 and total marks be 100.
Average = 52 => Total = 5200
Average of brightest 20 = 80=>Total marks scored by brightest 20 = 80*20 = 1600
Average of dullest 25 =31. => Total marks scored by dullest 25 = 25*31= 775
Marks scored by remaining 55 = 5200 -1600 - 775 = 2825
Average = 2825/55 = 51.4 % (Approx.)
Option B is the right answer.
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