Use a compass to draw a circle. The distance between the two legs of the compass is 2.5 cm. What is the diameter of the circle in cm?
用圆规画圆，圆规两脚间的距离为2.5厘米，这个圆的直径是多少厘米．
<gadget id="calculator">2.5 * 2</gadget>
<output>5</output>

<result>5</result>