Xiao Ming runs to school and walks home, so it takes 30 minutes on the road. If he runs back and forth, it only takes 10 minutes on the road. How many minutes does it take if he walks to and from school?
小明跑步上学，步行回家，那么在路上共用30分钟，如果来回都跑步，那么在路上只要10分钟，如果上学放学都步行要用多少分钟．
<gadget id="calculator">30 - 10</gadget>
<output>20</output>

<gadget id="calculator">10 / 2</gadget>
<output>5</output>

<gadget id="calculator">20 + 5</gadget>
<output>25</output>

<gadget id="calculator">25 * 2</gadget>
<output>50</output>

<result>50</result>