If a product is sold at the original price, it can make a profit of 25%. Later, the cost rises. Even if the selling price is increased by 20%, it can only make a profit of 20%. Find the percentage increase in the cost.
一种商品按原价出售可以获利25%，后来成本上升，虽将售价提高20%，也只能获利20%，求成本上升了百分之几．
<gadget id="calculator">25 / 100</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 + (1/4)</gadget>
<output>5/4 = around 1.25</output>

<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">(6/5) / (6/5)</gadget>
<output>1</output>

<gadget id="calculator">(5/4) * 1</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">(5/4) - 1</gadget>
<output>1/4 = around 0.25</output>

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