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% of a mean score of 31. The mean score of remaining 55% is
A. 40.8 approx
B. 45.3 approx
C. 51.4 approx
D. 53.8 approx
Ans: C.Sol.
Let the required mean score be x. Then,
20 × 80 + 25 × 31 + 55 × x = 52 × 100
⇔ 1600 + 775 + 55x = 5200
⇔ 55x = 2825
⇔ x = 565 / 11 = 51.4.
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