Chapter 4: Quadratic Equations

Example 9. If the list price of a book is reduced by Rs. 5, a person can buy 5 more books for Rs.300. Find the original list price of the book.

Soltution:- Let the original price of the book be Rs. x.

Then the reduced price of the book = Rs. ( x - 5)

Total amount = Rs. 300

According to the question

Or,

Or,

Or, 5(x² - 5x) = 1500

Or, x² - 5x = 300

Or, x² - 5x - 300 = 0

Or, x² - 20x + 15x - 300 = 0

Or, x(x - 20) + 15 (x - 20) = 0

Or, (x - 20) ( x + 15) = 0

x = -15, 20

As price can not be negative x = Rs. 20.