A and B are on a circular runway. It takes A 4 minutes to complete a lap and B 5 minutes to complete a lap. Two people run from the same place to the same direction at the same time, how many minutes will they meet again?
甲、乙两人在环形跑道上．甲跑完一圈需4分钟，乙跑完一圈需5分钟．两人从同一地点同时向同一个方向跑，多少分钟再一次相遇？
<gadget id="calculator">1 / 4</gadget>
<output>1/4 = around 0.25</output>

<gadget id="calculator">1 / 5</gadget>
<output>1/5 = around 0.2</output>

<gadget id="calculator">(1/4) - (1/5)</gadget>
<output>1/20 = around 0.05</output>

<gadget id="calculator">1 / (1/20)</gadget>
<output>20</output>

<result>20</result>