Kindle eTextbooks at Amazon Up to 80% off

As one of its daily deals, Amazon takes up to 80% off a selection of Kindle eTextbooks. That drops most titles to less than half the price of their paperback equivalents. Deal ends today. A couple of best bets, compared to their paperback editions:

• Karl F. Kuhn's Basic Physics Kindle eBook for $4.99 (pictured, low by $7)
• Hadnagy's Social Engineering: The Art of Human Hacking Kindle eBook for $6.99 (low by $18)