A commodity with a purchase price of $400 and a selling price of $500. How much profit is obtained from this commodity as a percentage of the cost.
一种商品，进货价400元，售价500元．这种商品所获得的利润占成本的多少．
<gadget id="calculator">500 - 400</gadget>
<output>100</output>

<gadget id="calculator">100 / 400</gadget>
<output>1/4 = around 0.25</output>

<result>1/4 = around 0.25</result>