Students from classes A and B went to the Children's Palace to participate in activities, but there was only one car to pick them up. When the students in Class A leave the school by car, the students in Class B start to walk. The students in Class A get off at a certain place on the way and walk. The bus returns immediately to pick up the students in Class B, and they drive directly to the Children's Palace. It is known that the walking speed of the students is 4 kilometers per hour, the speed of the students in the car is 40 kilometers per hour, and the speed of the empty car is 50 kilometers per hour. To make the two classes of students arrive at the Children's Palace at the same time, what percentage of the whole journey should the students of Class A walk?
甲乙两班学生到少年宫参加活动，但只有一辆车接送．甲班学生坐车从学校出发的同时乙班学生开始步行，车到途中某处甲班学生下车步行，车立即返回接乙班学生上车，并直接开往少年宫．已知学生步行速度为每小时4千米，汽车载学生时速度为每小时40千米，空车时速度为每小时50千米．要使两班学生同时到达少年宫，甲班学生应步行全程的几分之几？
<gadget id="calculator">1 / 40</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">1 / 50</gadget>
<output>1/50 = around 0.02</output>

<gadget id="calculator">(1/40) + (1/50)</gadget>
<output>9/200 = around 0.045</output>

<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">2 / 50</gadget>
<output>1/25 = around 0.04</output>

<gadget id="calculator">(1/4) + (1/40) + (1/25)</gadget>
<output>63/200 = around 0.315</output>

<gadget id="calculator">(9/200) / (63/200)</gadget>
<output>1/7 = around 0.142857</output>

<result>1/7 = around 0.142857</result>