On a map with a scale of 1:4,000,000, the distance between A and B is 2.5 cm. How many hours does it take for a car with a speed of 50 kilometers per hour to go back and forth between A and B?
在比例尺为1：4000000的地图上，量得甲、乙两城的距离是2.5厘米一辆速度为每小时50千米的汽车在甲、乙两城之间往返一趟需多少小时．
<gadget id="calculator">1 / 4_000_000</gadget>
<output>1/4_000_000 = around 0</output>

<gadget id="calculator">2.5 / (1/4_000_000) / 100_000 / 50</gadget>
<output>2</output>

<gadget id="calculator">2 * 2</gadget>
<output>4</output>

<result>4</result>