Grandma Wang’s family raises 30 chickens and ducks. There are 10 more chickens than ducks. How many ducks are there?
王奶奶家养鸡、鸭共30只，鸡比鸭多10只，养鸭多少只．
<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">20 / 2</gadget>
<output>10</output>

<result>10</result>