Question
The average number of novels on historical, thriller and fantasy in a library is 160, and the average number of novels on historical and fantasy is 155. If the number novels on fantasy is 30% less than the number of novels on thriller, then what is the number of novels on historical in the library?
Solution
Let the number of novels on historical, thriller and fantasy be x, y and z respectively. Given, (x + y + z)/3 = 160 => x + y + z = 480 ….. (1) And, (x + z)/2 = 155 => x + z = 310 ….. (2) From equation 1 and 2 Number of novels on thriller = y = 170 Number of novels on fantasy = 0.7 × 170 = 119 Therefore, number of novels on historical = 480 – (170 + 119) = 191
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