A shopkeeper buys some books for rupees 80 if he had bought 4 more books for the same amount each book would have cost Rupees 1 less find the number of books he bought
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let shopkeeper buys books = x
total cost = 80
cost of a book = 80/x
according to given condition
(x+4) * (( 80/x) - 1) = 80
(x+4)*(80-1x) = 80x
80x - x2 + 320 - 4x = 80x
-x2 +320 -4x =0
x2+ 4x - 320 =0
x2+ 20x - 16x -320=0
x( x+20) -16 ( x+20) =0
(x+20) (x-16)=0
x= -20 / x=16
A shopkeeper buys 16 books
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