Take a copper wire and wind it 10 times on a circular tube with a diameter of 10 cm. How many centimeters is the length of the copper wire?
用一根铜丝，正好在一个直径是10厘米的圆管上绕上10圈，这根铜丝约长多少厘米．
<gadget id="calculator">3.14 * 10 * 10</gadget>
<output>314</output>

<result>314</result>