Uncle Zhang’s family has some chickens. There are 400 roosters, 20% less than hens. How many hens are there? (column equation solution)
张大伯家养了一些鸡，公鸡有400只，比母鸡少20%，母鸡有多少只？(列方程解答)
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1 - (1/5)</gadget>
<output>4/5 = around 0.8</output>

<gadget id="calculator">400 / (4/5)</gadget>
<output>500</output>

<result>500</result>