Mr. Li takes a car when he goes to work, and walks when he gets off work. It takes 50 minutes on the road. If he walks both ways, it will take 80 minutes. How many minutes will it take if you take a car to and fro.
李老师上班时坐车，下班时步行，在路上共用50分钟，如果往返都步行要用80分钟．如果往返都坐车，只需多少分钟．
<gadget id="calculator">80 / 2</gadget>
<output>40</output>

<gadget id="calculator">50 - 40</gadget>
<output>10</output>

<gadget id="calculator">10 * 2</gadget>
<output>20</output>

<result>20</result>