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    Question

    If average weight of a class is ‘y’ kg. If a new student weighing 21 kg took admission, then the average weight is increases by 1 kg. If the weight of this student had been 16 kg then the average weight of the class would have decreased by 2 kg. Find ‘y’.

    A 12 Correct Answer Incorrect Answer
    B 24 Correct Answer Incorrect Answer
    C 18 Correct Answer Incorrect Answer
    D 15 Correct Answer Incorrect Answer
    E 21 Correct Answer Incorrect Answer

    Solution

    Let the number of students in a class be x. Therefore, the total weight = xy According to question, => (x + 1) (y + 1) = xy + 21 => xy + x + y + 1 = xy + 21 => x + y = 20 ------ (i) If the weight of this student had been 18 kg then the average weight of the class would have decreased by 2 kg. => (x + 2) (y – 2) = xy + 16 => xy + 2y – 2x – 4 = xy + 16 => y – x = 10 ------ (ii) Solving (i) and (ii), we get => 2y = 30 => y = 15

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