In a farm, the number of ducks is 20% less than the number of chickens, and the number of chickens is 1000 more than that of ducks. How many ducks are raised in this farm?
一个养殖场，养鸭的只数比养鸡的只数少20%，养的鸡比鸭多1000只．这个养殖场养鸭多少只？
<gadget id="calculator">20 / 100</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">1_000 / (1/5)</gadget>
<output>5_000</output>

<gadget id="calculator">5_000 - 1_000</gadget>
<output>4_000</output>

<result>4_000</result>