Xiao Ming's home is 400 meters away from school. If he walks 80 meters per minute, how long will it take him to walk back and forth twice a day?
小明家到学校有400米，如果每分钟走80米，他每天走两个来回，共需要多长时间？
<gadget id="calculator">2 / 80</gadget>
<output>1/40 = around 0.025</output>

<gadget id="calculator">400 * 2 * (1/40)</gadget>
<output>20</output>

<result>20</result>