On a drawing with a scale of 1:500, the diameter of a semicircular flower bed is measured to be 4 cm. Find the perimeter of this flower bed.
在一张比例尺是1：500的图纸上，量得一个半圆形花坛的直径是4厘米．求这个花坛的周长．
<gadget id="calculator">62.8 / 2</gadget>
<output>31.4</output>

<gadget id="calculator">1 / 500</gadget>
<output>1/500 = around 0.002</output>

<gadget id="calculator">4 / (1/500) / 100</gadget>
<output>20</output>

<gadget id="calculator">31.4 + 20</gadget>
<output>51.4</output>

<result>51.4</result>