The store sells a football for 30 yuan and earns 30% of the price. Now it sells it for 24.5 yuan. Is it a profit or a loss? How much did you lose or make?
商店30元卖出一个足球，赚了售价的30%，现在以24.5元卖出，是赚还是赔？赔或赚了多少？
<gadget id="calculator">30 / 100</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">30 * (7/10)</gadget>
<output>21</output>

<gadget id="calculator">24.5 - 21</gadget>
<output>3.5</output>

<result>3.5</result>