There are 210 fewer chickens than ducks, and the ratio of the number of chickens to the number of ducks is 2:5. How many ducks are there?
鸡比鸭少210只，鸡的只数和鸭的只数比是2：5．鸭有多少只？
<gadget id="calculator">5 - 2</gadget>
<output>3</output>

<gadget id="calculator">210 / 3</gadget>
<output>70</output>

<gadget id="calculator">70 * 5</gadget>
<output>350</output>

<result>350</result>