The perimeter of an isosceles triangle is 100 cm and the base is 40 cm long. What is the waist length of this triangle?
等腰三角形的周长是100厘米，底边长40厘米，这个三角形的腰长是多少厘米？
<gadget id="calculator">100 - 40</gadget>
<output>60</output>

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<result>30</result>