Question
The average number of books on history, polity and
geography in a library is 144, and the average number of books on history and geography is 140. If the number books on geography is 25% 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 = 144 Or, x + y + z = 432 ….. (1) And, (x + z)/2 = 140 Or, x + z = 280 ….. (2) From equation 1 and 2 Number of books on polity = y = 152 Number of books on geography = 0.75 × 152 = 114 Therefore, number of books on history = 432 – (152 + 114) = 166
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