It takes 3 minutes for a train to pass through the 2400-meter bridge, but it only takes 1 minute to pass by a power pole on the side of the road at the same speed. Find the length of this train.
一列火车通过2400米的大桥需要3分钟，用同样的速度从路边的一根电线杆旁边通过，只用了1分钟．求这列火车的长度．
<gadget id="calculator">3 - 1</gadget>
<output>2</output>

<gadget id="calculator">2_400 / 2</gadget>
<output>1_200</output>

<gadget id="calculator">1_200 * 1</gadget>
<output>1_200</output>

<result>1_200</result>