# A shopkeeper buys a number of books for Rs. 1200. If he had bought 10 more books for the same amount, each book would have cost Rs. 20 less. How many books did he buy?

Let x be the no. of books and y is the cost of each book. ––––––(1)

when 10 more students appear then, ––––(2)

On solving both (1) and (2) equation

subtracting (2) from (1)   600 = x2 + 10x

x2 + 10x – 600 = 0

On applying Sreedhracharya formula     X = – 30 or X = 20 The number of books, he purchased are 20. (as only positive values are considered).

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