A train is 400 meters long, and the distance between the poles along the railway line is 40 meters. It took 2 minutes for the train to reach the first pole and leave the 51st pole. How many kilometers per hour does the train travel?
一列火车长400米，铁路沿线的电线杆间隔都是40米，这列火车从车头到达第1根电线杆到车尾离开第51根电线杆用了2分钟．这列火车每小时行多少千米？
<gadget id="calculator">1 / 30</gadget>
<output>1/30 = around 0.033333</output>

<gadget id="calculator">2.4 / (1/30)</gadget>
<output>72</output>

<result>72</result>