John's weight bench can support 1000 pounds.  He wants to make sure to stay 20% under that weight for safety.  If he weighs 250 pounds how much weight can he put on the bar?
He wants to stay 1000*.2=
<gadget id="calculator">1000*.2</gadget>
<output>200</output>
200 pounds under the max.
So he wants to stay under 1000-200=
<gadget id="calculator">1000-200</gadget>
<output>800</output>
800 pounds.
That means he can put 800-250=
<gadget id="calculator">800-250</gadget>
<output>550</output>
550 pounds on the bar.

<result>550</result>