The ratio of two unequal sides in an isosceles triangle is 1:2, and the circumference is 40 cm. How long is the waist of this triangle in cm?
等腰三角形中不相等的两条边的比是1：2，周长为40厘米，则这个三角形的腰长多少厘米？
<gadget id="calculator">1 + 2 + 2</gadget>
<output>5</output>

<gadget id="calculator">2 / 5</gadget>
<output>2/5 = around 0.4</output>

<gadget id="calculator">40 * (2/5)</gadget>
<output>16</output>

<result>16</result>