The earth's surface area is about 510 million square kilometers, of which about (3/10) is land, and the rest is ocean. How many square kilometers is the ocean area on Earth?
地球的表面积大约是51000万平方千米，其中约(3/10)是陆地，其余的是海洋．地球上海洋面积大约是多少万平方千米？
<gadget id="calculator">3 / 10</gadget>
<output>3/10 = around 0.3</output>

<gadget id="calculator">1 - (3/10)</gadget>
<output>7/10 = around 0.7</output>

<gadget id="calculator">51_000 * (7/10)</gadget>
<output>35_700</output>

<result>35_700</result>