Uncle Zhang has 400 chickens, which is 1/5 less than ducks. How many ducks are there? What is the correct column
张大爷养的鸡有400只，比鸭少(1/5)，鸭有多少只？正确的列式是多少
<gadget id="calculator">1 / 5</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>