Xiao Ming runs a distance in three equal periods of time. It is known that his average speed in each period of time is 9 kilometers, 8 kilometers and 7 kilometers per hour respectively. Find the average speed of Xiaoming running this distance.
小明在三段相等的时间内跑完一段路程．已知他在每段时间内的平均速度分别是每小时跑9千米、8千米和7千米，求小明跑这段路程的平均速度．
<gadget id="calculator">9 + 8 + 7</gadget>
<output>24</output>

<gadget id="calculator">24 / 3</gadget>
<output>8</output>

<result>8</result>