The lengths of three ribbons are 17cm, 24cm, and 16cm respectively. What is the average length of these three ribbons?
三条丝带分别长17cm、24cm、16cm，这三条丝带的平均长度是多少．
<gadget id="calculator">17 + 24 + 16</gadget>
<output>57</output>

<gadget id="calculator">57 / 3</gadget>
<output>19</output>

<result>19</result>