A circular ring with an outer diameter of 4 cm is made from a steel bar with a diameter of 5 mm. What is the length of a steel chain composed of 10 such rings?
用直径为5毫米的钢筋做成外直径为4厘米的圆环，由10个这样的圆环构成的钢链长多少分米．
<gadget id="calculator">5 / 10</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">4 - (1/2) - (1/2)</gadget>
<output>3</output>

<gadget id="calculator">4 - 3</gadget>
<output>1</output>

<gadget id="calculator">4 - 1</gadget>
<output>3</output>

<gadget id="calculator">10 - 1</gadget>
<output>9</output>

<gadget id="calculator">3 * 9</gadget>
<output>27</output>

<gadget id="calculator">4 + 27</gadget>
<output>31</output>

<gadget id="calculator">31 / 10</gadget>
<output>31/10 = around 3.1</output>

<result>31/10 = around 3.1</result>