There are 4 colored ribbons, the lengths are: 15 cm, 17 cm, 22 cm, 18 cm, what is the average length of these 4 colored ribbons in cm?
有4根彩带，长度分别为：15厘米、17厘米、22厘米、18厘米，这4根彩带的平均长度是多少厘米．
<gadget id="calculator">15 + 17 + 22 + 18</gadget>
<output>72</output>

<gadget id="calculator">72 / 4</gadget>
<output>18</output>

<result>18</result>