The arithmetic mean of the scores of a group of students in an exam was 61. The brightest 20% of them secured a mean score of 80 and the dullest 25% a mean score of 31. The mean score of the remaining 55% is:  Choose the correct choice from the following:
A) 45	B) 50	C) 67.72 approximately	D) 74.6 approximately	E) None of these
Let the required mean score be x. Then, 20 x 80 + 25 x 31 + 55 x x = 61 x 100   1600 + 775 + 55x = 6100   55x = 3725   x = 3725/55 = 67.72   Answer : 67.72 approximately
<result>C</result>
The arithmetic mean of the scores of a group of students in an exam was 61. The brightest 20% of them secured a mean score of 80 and the dullest 25% a mean score of 31. The mean score of the remaining 55% is: