After selling (5/7) of the total number of chickens in a chicken farm, there are still 1200 chickens left. How many chickens are there in the chicken farm?
一个养鸡场卖出鸡的总数的(5/7)后，还剩1200只，养鸡场原来有多少只鸡．
<gadget id="calculator">5 / 7</gadget>
<output>5/7 = around 0.714286</output>

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

<gadget id="calculator">1_200 / (2/7)</gadget>
<output>4_200</output>

<result>4_200</result>