Two gears mesh with each other, the radius of the big gear is 20 cm. When the large gear rotates 4 times, the small gear rotates 10 times, what is the radius of the small gear in centimeters?
两个相互咬合的齿轮，大齿轮的半径是20厘米．当大齿轮转4周时，小齿轮转了10周，小齿轮的半径多少厘米？
<gadget id="calculator">2 * 3.14 * 20 * 4</gadget>
<output>502.4</output>

<gadget id="calculator">2 * 3.14 * 10</gadget>
<output>62.8</output>

<gadget id="calculator">502.4 / 62.8</gadget>
<output>8</output>

<result>8</result>