The perimeter of an isosceles triangle is 40cm, and the ratio of a pair of adjacent sides is 2:1, what is the length of its waist in centimeters?
一个等腰三角形的周长是40cm，一组邻边的比是2：1，它的腰长多少厘米．
<gadget id="calculator">2 + 2 + 1</gadget>
<output>5</output>

<gadget id="calculator">40 / 5</gadget>
<output>8</output>

<gadget id="calculator">8 * 2</gadget>
<output>16</output>

<result>16</result>