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    Question

    The average number of books on history, polity and

    geography in a library is 120, and the average number of books on history and geography is 130. If the number books on geography is 20% less than the number of books on polity, then what is the number of books on history in the library?
    A 150 Correct Answer Incorrect Answer
    B 130 Correct Answer Incorrect Answer
    C 180 Correct Answer Incorrect Answer
    D 170 Correct Answer Incorrect Answer

    Solution

    Let the number of books on History, Polity and Geography be x, y and z respectively. Given, (x + y + z)/3 = 120 Or, x + y + z = 360 тАж.. (1) And, (x + z)/2 = 130 Or, x + z = 260 тАж.. (2) From equation 1 and 2 Number of books on polity = y = 100 Number of books on geography = 0.8 ├Ч 100 = 80 Therefore, number of books on history = 360 тАУ (100 + 80) = 180

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