How many square centimeters of cardboard is needed to make a cylinder with base diameter and height of 5 cm out of cardboard?
用硬纸板做一个底面直径和高都是5厘米的圆柱，至少需要硬纸板多少平方厘米．
<gadget id="calculator">3.14 * 5 * 5</gadget>
<output>78.5</output>

<gadget id="calculator">5 / 2</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">(5/2) ** 2</gadget>
<output>25/4 = around 6.25</output>

<gadget id="calculator">3.14 * (25/4) * 2</gadget>
<output>39.25</output>

<gadget id="calculator">78.5 + 39.25</gadget>
<output>117.75</output>

<result>117.75</result>