John buys 500 newspapers.  Each newspaper sells for $2.  He sells 80% of them.  He buys them all for 75% less than the price at which he sells them.  How much profit does he make?
He sells 500*.8=
<gadget id="calculator">500*.8</gadget>
<output>400</output>
400 newspapers.
He sells them for 400*2=$
<gadget id="calculator">400*2</gadget>
<output>800</output>
800.
He gets a discount of 2*.75=$
<gadget id="calculator">2*.75</gadget>
<output>1.5</output>
1.5 on the newspapers.
So he buys them for 2-1.5=$
<gadget id="calculator">2-1.5</gadget>
<output>0.5</output>
.5.
So he spent 500*.5=$
<gadget id="calculator">500*.5</gadget>
<output>250</output>
250 buying them.
That means he made a profit of 800-250=$
<gadget id="calculator">800-250</gadget>
<output>550</output>
550.

<result>550</result>