cyclist and a pedestrian are traveling in the same direction on a street, and the speed of the cyclist is three times that of the pedestrian. Every 10 minutes a bus passes a pedestrian, and every 20 minutes a bus passes a cyclist. If a bus departs from the departure station at the same interval each time, how many minutes does a bus depart?
一条街上，一个骑车人和一个步行人同向而行，骑车人的速度是步行人速度的3倍．每隔10分钟有一辆公共汽车超过步行人，每隔20分钟，有一辆公共汽车超过骑车人．如果公共汽车从始发站每次间隔同样的时间发一辆车，那么每隔多少分钟发一辆公共汽车．
<gadget id="calculator">1 / 10</gadget>
<output>1/10 = around 0.1</output>

<gadget id="calculator">1 / 20</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/10) - (1/20)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">(1/20) / 2</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">(1/40) + (1/10)</gadget>
<output>1/8 = around 0.125</output>

<gadget id="calculator">1 / (1/8)</gadget>
<output>8</output>

<result>8</result>