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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:

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Rs. 15

Rs. 20

Rs. 25

Rs. 30

answer is B.

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Detailed Solution

Concep-The total amount of money required for a manufacturer to produce a specific good or provide a specific service is known as the cost price.
Let the book's original list price be = Rs. x
Number of books originally purchased

= 300 x

When the price of the book is reduced by 5
A new number of books will be purchased

= 300 x − 5

Original number of books purchased-New number of books purchased

= 5

∴ 300 x − 5 − 300 x = 5

⇒ 300 x − 300 x + 1500 x (x − 5) = 5

⇒ x 2 − 5 x = 300

⇒ x 2 − 20 x + 15 x − 300 = 0

⇒ x (x − 20) + 15 (x − 20) = 0

⇒ (x − 20) (x + 15) = 0

⇒ x − 20 = 0

x + 15 = 0

⇒ x = 20

x = − 15

∴ x = 20

The price of the book upon launch was Rs 20.
Hence, the correct option is 2.

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