ship sails back and forth between ports A and B, traveling 36 kilometers per hour downstream and 24 kilometers per hour upstream, what is the average speed of the ship traveling between ports A and B?
一艘船在甲、乙两港间往返航行，顺流每小时行36千米，逆流每小时行24千米，这艘船在甲、乙两港间往返的平均速度是多少？
<gadget id="calculator">36 + 24</gadget>
<output>60</output>

<gadget id="calculator">60 / 2</gadget>
<output>30</output>

<result>30</result>