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    Question

    The average number of books on history, polity and

    geography in a library is 110, and the average number of books on history and geography is 120. If the number books on geography is 30% less than the number of books on polity, then what is the number of books on history in the library?
    A 157 Correct Answer Incorrect Answer
    B 167 Correct Answer Incorrect Answer
    C 177 Correct Answer Incorrect Answer
    D 187 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 = 110 Or, x + y + z = 330 ….. (1) And, (x + z)/2 = 120 Or, x + z = 240 ….. (2) From equation 1 and 2 Number of books on polity = y = 90 Number of books on geography = 0.7 × 90 = 63 Therefore, number of books on history = 330 – (90 + 63) = 177

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