What is the average of the seven numbers 18, 19, 20, 21, 22, 23, and 24?
18，19，20，21，22，23，24这七个数的平均数是多少．
<gadget id="calculator">18 + 19 + 20 + 21 + 22 + 23 + 24</gadget>
<output>147</output>

<gadget id="calculator">147 / 7</gadget>
<output>21</output>

<result>21</result>