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    Question

    The average number of books on history, polity and

    geography in a library is 165, and the average number of books on history and geography is 140. 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 108 Correct Answer Incorrect Answer
    B 128 Correct Answer Incorrect Answer
    C 138 Correct Answer Incorrect Answer
    D 118 Correct Answer Incorrect Answer
    E None of these 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 = 165 Or, x + y + z = 495 ….. (1) And, (x + z)/2 = 140 Or, x + z = 280 ….. (2) From equation 1 and 2 Number of books on polity = y = 215 Number of books on geography = 0.8 × 215 = 172 Therefore, number of books on history = 495 – (215 + 172) = 108

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