A set of numbers: 17, 19, 21, 23, 25, 27, 29, what is the average of this set of numbers.
一组数：17，19，21，23，25，27，29，这组数的平均数是多少．
<gadget id="calculator">17 + 19 + 21 + 23 + 25 + 27 + 29</gadget>
<output>161</output>

<gadget id="calculator">161 / 7</gadget>
<output>23</output>

<result>23</result>