Xiaodong’s family raises 500 chickens, and the number of ducks is 20% less than that of chickens. How many ducks does Xiaodong’s family raise?
小东家养鸡500只，鸭的只数比鸡少20%，小东家养鸭多少只？
<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">500 * (4/5)</gadget>
<output>400</output>

<result>400</result>