Xiao Ming rides a bicycle from his home to the bookstore. He travels an average of 320 meters per minute, arrives in 15 minutes, and only takes 12 minutes to return by the original road. How many meters per minute on average?
小明骑车从家到书店，平均每分钟行320米，15分钟到达，原路返回只用12分钟，平均每分钟行多少米？
<gadget id="calculator">15 / 12</gadget>
<output>5/4 = around 1.25</output>

<gadget id="calculator">320 * (5/4)</gadget>
<output>400</output>

<result>400</result>