There are 210 ducks, and the ratio of the number of chickens to the number of ducks is 2:5. How many chickens are there?
鸭有210只，鸡的只数和鸭的只数比是2：5．鸡有多少只？
<gadget id="calculator">2 + 5</gadget>
<output>7</output>

<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

<gadget id="calculator">210 / (5/7)</gadget>
<output>294</output>

<gadget id="calculator">1 - (5/7)</gadget>
<output>2/7 = around 0.285714</output>

<gadget id="calculator">294 * (2/7)</gadget>
<output>84</output>

<result>84</result>