A librarian purchased 60 story books for his library. But

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A librarian purchased 60 story books for his library. But he found that he could get 4 extra books by spending Rs. 336 more and then the overall average price per book would be reduced by Re 1. The previous average price of each book was

1. Rs. 84
2. Rs. 83
3. Rs. 68
4. Rs. 100

Correct Option: D

Let the previous average price be Rs. p.
According to the question,
⇒ 60p + 336 = (p – 1) 64
⇒ 60p + 336 = 64p – 64
⇒ 64p – 60p = 336 + 64
⇒ 4p = 400
⇒ p = 400 ÷ 4 = Rs. 100