Question
The average number of books on history, polity and
geography in a library is 180, 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?Solution
Let the number of books on History, Polity and Geography be x, y and z respectively. Given, (x + y + z)/3 = 180 Or, x + y + z = 540 ….. (1) And, (x + z)/2 = 150 Or, x + z = 300 ….. (2) From equation 1 and 2 Number of books on polity = y = 240 Number of books on geography = 0.8 × 240 = 192 Therefore, number of books on history = 540 – (240 + 192) = 108
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