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Let, number of book and number of pen sold by shopkeeper be 21x and 12x respectively. Number of pencil sold by shopkeeper = 11/4 × 12x = 33x So, 21x × 40 + 12x × 20 + 33x × 10 = 21150 ⇒ 840x + 240x + 330x = 21150 ⇒ 1410x = 21150 x = 15 Number of pen sold by shopkeeper = 12x = 180