# On selling a pen at 5% loss and a book at 15% gain, Karim gains Rs. 7. If he sells the pen at 5% gain and the book at 10% gain, he gains Rs. 13. What

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On selling a pen at 5% loss and a book at 15% gain, Karim gains Rs. 7. If he sells the pen at 5% gain and the book at 10% gain, he gains Rs. 13. What is the cost price of the book in Rupees?
1. 100
2. 80
3. 85
4. 95

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Correct Answer - Option 2 : 80

Calculation:

Let CP of the pen be P

CP of the book be B

According to question,

⇒ -0.05P + 0.15B = 7      ____(i)

Now, If he sells the pen at 5% gain and the book at 10% gain

⇒ 0.05P + 0.10B = 13      ____(ii)

Adding equation (i) and (ii) we get,

⇒ 0.25B = 20

⇒ B = 80

∴ CP of book is 80.