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    Question

    A group of students consists of 25 boys and the rest are

    girls. The average marks scored by boys is 72, and the average marks scored by girls is 84. If the average marks of the entire group is 78, find the number of girls in the group.
    A 20 Correct Answer Incorrect Answer
    B 25 Correct Answer Incorrect Answer
    C 10 Correct Answer Incorrect Answer
    D 18 Correct Answer Incorrect Answer
    E 12 Correct Answer Incorrect Answer

    Solution

    Let the number of girls be g. The total number of students = 25 + g. The total marks of boys = 25 × 72 = 1800. The total marks of girls = g × 84. The total marks of the group = 78 × (25 + g). From the data: 1800 + 84g = 78(25 + g). 1800 + 84g = 1950 + 78g. 84g - 78g = 1950 - 1800. 6g = 150. g = 150 / 6 = 25. Correct option: b

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