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?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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