Question
The average number of novels on historical, thriller and
fantasy in a library is 25, and the average number of novels on historical and fantasy is 20. If the number novels on fantasy is 25% 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 = 25 => x + y + z = 75 ….. (1) And, (x + z)/2 = 20 => x + z = 40 ….. (2) From equation 1 and 2 Number of novels on thriller = y = 35 Number of novels on fantasy = 0.60 × 35 = 21 Therefore, number of novels on historical = 75 – (35 + 21) = 19
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