Paperbacks sell between $8 and $12 and there are altogether 200 paperbacks.

Hence

least price for the 200 paperbacks would be \(200 * 8 = 1600\)

While there are 100 hardcover and each sell for anything between $14 and $18

The least the hardcover could sell for is \(14* 100 = 1400\)

Therefore the least average would be \(\frac{1600+1400}{300} = 10\)

For any other combination of price for paperback and hardcover the avg would be more than 10

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This is my response to the question and may be incorrect. Feel free to rectify any mistakes