The cost of a pair of shoes is 100 yuan. If you sell it at 80% of the price, you can earn 20%. If you sell it at a 10% discount, how much can you earn?
一双鞋成本是100元，如果按标价的80%出售，可赚20%，那么若打九折出售，可赚多少
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 + (1/5)</gadget>
<output>6/5 = around 1.2</output>

<gadget id="calculator">80 / 100</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">(6/5) / (4/5)</gadget>
<output>3/2 = around 1.5</output>

<gadget id="calculator">90 / 100</gadget>
<output>9/10 = around 0.9</output>

<gadget id="calculator">100 * (3/2) * (9/10)</gadget>
<output>135</output>

<gadget id="calculator">135 - 100</gadget>
<output>35</output>

<gadget id="calculator">35 / 100</gadget>
<output>7/20 = around 0.35</output>

<result>7/20 = around 0.35</result>