A person bought a book and a novel for ₹2800. He sold the book at 10% profit and the novel at 12.5% profit. If his overall profit was 13%, then what is the difference between the cost prices of the book and the novel?

Using the method of alligation, the overall profit is 13 percent, with the book yielding 10 percent and the novel yielding 12.5 percent. The ratio of the cost price of the book to the novel is (13 minus 12.5) to (13 minus 10), which simplifies to 0.5 to 3, or 1 to 6. The total cost is 2800 rupees, so the cost price of the book is (1 divided by 7) multiplied by 2800, resulting in 400 rupees, and the cost price of the novel is (6 divided by 7) multiplied by 2800, resulting in 2400 rupees. The difference between the cost prices is 2400 minus 400, which equals 400 rupees.

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