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    Question

    The average marks of 30 students in Class I is 60. The

    average marks of some students in Class II is 75. When all students of both classes are taken together, the overall average becomes 69. Find the number of students in Class II.
    A 25 Correct Answer Incorrect Answer
    B 37 Correct Answer Incorrect Answer
    C 45 Correct Answer Incorrect Answer
    D 66 Correct Answer Incorrect Answer

    Solution

    Let number of students in Class II = x Total marks of Class I = 30 × 60 = 1800 Total marks of Class II = 75x Overall average = 69: (1800 + 75x) / (30 + x) = 69 1800 + 75x = 69(30 + x) 1800 + 75x = 2070 + 69x 75x − 69x = 2070 − 1800 6x = 270 ⇒ x = 45 Answer: Class II has 45 students.

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