There are 2,400 chickens and ducks in a farm. The ratio of chickens to ducks is 8:7. After selling some chickens, the ratio of chickens to ducks is 1:2. How many chickens were sold?
一个养殖场有鸡和鸭共2400只，其中鸡与鸭的只数比是8：7，卖掉一些鸡后，鸡与鸭的只数比是1：2，卖掉了多少只鸡？
<gadget id="calculator">8 + 7</gadget>
<output>15</output>

<gadget id="calculator">8 / 15</gadget>
<output>8/15 = around 0.533333</output>

<gadget id="calculator">2_400 * (8/15)</gadget>
<output>1_280</output>

<gadget id="calculator">7 / 15</gadget>
<output>7/15 = around 0.466667</output>

<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2_400 * (7/15) * (1/2)</gadget>
<output>560</output>

<gadget id="calculator">1_280 - 560</gadget>
<output>720</output>

<result>720</result>