Mark has the option of getting a $300 lens with a 20% discount or a $220 lens.  How much money does he save by buying the cheaper lens?
The discount is worth 300*.2=$
<gadget id="calculator">300*.2</gadget>
<output>60</output>
60.
So the lens cost 300-60=$
<gadget id="calculator">300-60</gadget>
<output>240</output>
240.
That means he saves 240-220=$
<gadget id="calculator">240-220</gadget>
<output>20</output>
20 by buying the cheaper lens.

<result>20</result>