Question

pls answer...............

Answer 1

Answer:

15 books are purchased

Step-by-step explanation:

Let n be the number of books purchased.

Let c be the cost of one book.

We are given that n books cost 60, so...

nc = 60      ... (1)

We are also given that if the cost were c-1 then we would get n+5 books for the same amount, so...

(n+5)(c-1) = 60      ... (2)

Putting (1) and (2) together gives

(n+5)(c-1) = nc

=> nc - n + 5c - 5 = nc

=> n - 5c + 5 = 0

=> n² - 5nc + 5n = 0     [ multiplied by -n ]

=> n² - 5×60 + 5n = 0    [ used (1) ]

=> n² + 5n - 300 = 0

=> ( n - 15 ) ( n + 20 ) = 0

=> n = 15 or n = -20

=> n = 15, since n cannot be negative.