Question

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

• A. Rs 15
• B. Rs 20
• C. Rs 25
• D. Rs 30

Answer 1

Answer: (B)

Rs 20

Let the original list price of the book be=Rs x

Original number of books purchased=$\frac{300}{x}$

When the price of the book is reduced by 5

New Number of books purchased will be=$\frac{300}{x-5}$

New number of books purchased-Original number of books purchased=5

$\therefore \frac{300}{x-5}-\frac{300}{x}=5$

$\Rightarrow \frac{300x-300x+1500}{x(x-5)}=5$

$\Rightarrow x^2-5x=300$

$\Rightarrow x^2-20x+15x-300=0$

$\Rightarrow x(x-20)+15(x-20)=0$

$\Rightarrow (x-20)(x+15)=0$

$\Rightarrow x-20=0orx+15=0$

$\Rightarrow x=20orx=-15$

$\therefore x=20$

the original cost of book is Rs 20