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    Question

    The average number of books on history, polity and

    geography in a library is 140, and the average number of books on history and geography is 150. 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 214 Correct Answer Incorrect Answer
    B 224 Correct Answer Incorrect Answer
    C 204 Correct Answer Incorrect Answer
    D 164 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 = 140 Or, x + y + z = 280 ….. (1) And, (x + z)/2 = 150 Or, x + z = 300 ….. (2) From equation 1 and 2 Number of books on polity = y = 120 Number of books on geography = 0.8 × 120 = 96 Therefore, number of books on history = 420 – (120 + 96) = 204

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