Mark has the option of getting a $300 lens with a 20% discount or a $220 lens. How much money does he save by buying the cheaper lens? Let's be accurate as possible.
The discount is worth 300 * .2 = $60. So the lens cost 300 - 60 = $240. That means he saves 240 - 220 = $20 by buying the cheaper lens.
The answer: 20.