The arithmetic mean of the scores of a group of students in a test was 70. 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? Select the correct option:
A) A)71.4. B) B)91.7 C) C)84.09 D) D)81.1 E) E)71.2
Let the required means score be x. Then,   20 * 80 + 25 * 31 + 55 * x = 70 * 100   = 1600 + 775 + 55x = 7000   = 55x = 4625   = x = 84.09   Answer:84.09
<result>C</result>
The arithmetic mean of the scores of a group of students in a test was 70. 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?