If the cost of a commodity is reduced by 10%, while the selling price remains the same, its profitability will increase by 15 percentage points. Find the profit rate after reducing the cost of the commodity.
如果一种商品的成本降低10%，而售价不变，那么其盈利率将提高15个百分点．求该商品成本降低后的盈利率．
<gadget id="calculator">15 / 100</gadget>
<output>3/20 = around 0.15</output>

<gadget id="calculator">10 / 100</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(1/10) * (3/20)</gadget>
<output>3/200 = around 0.015</output>

<gadget id="calculator">(3/20) - 1 - (1/10) - (3/200)</gadget>
<output>-193/200 = around -0.965</output>

<gadget id="calculator">1 + (-193/200)</gadget>
<output>7/200 = around 0.035</output>

<gadget id="calculator">(1/10) - 1</gadget>
<output>-9/10 = around -0.9</output>

<gadget id="calculator">1 + (-9/10)</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">(7/200) / (1/10)</gadget>
<output>7/20 = around 0.35</output>

<gadget id="calculator">(7/20) + (3/20)</gadget>
<output>1/2 = around 0.5</output>

<result>1/2 = around 0.5</result>