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Question
A shopkeeper buys a number of books for Rs 840. If he had bought 5 more books for the same amount, each book would have cost Rs 4 less. How many books did he buy?
Solution
Let the num,ber of books be b.
Amount of each bok = `840/"b"`
If the number of books increased to B + 5 , it would have costed `840/"b" - 4`
As the amount is same , hence
`(840/"b" - 4)("b" + 5) = 840`
⇒ (840 - 4b)(b + 5) = 840b
⇒ 840b + 4200 - 4b2 - 20b = 840 b
⇒ (b + 35)(b - 30) = 0
Hence , no.of. books = 30
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