The two brothers took a taxi from point A to point B, and when they reached the midpoint of the two places, they met a classmate. In order to save money, the three of them ride together to point B, and the driver charges 20 yuan. If the fare is paid according to the distance traveled by each person, how much should the student who gets on the bus later pay?
兄弟两人乘一辆出租车从A地到B地，行驶到两地中点时，遇到一位同学．为了省钱，三人合乘到B地，司机收费20元．如果按每人乘车的路程来付车费，后上车的这位同学应付多少元？
<gadget id="calculator">1 / 2</gadget>
<output>1/2 = around 0.5</output>

<gadget id="calculator">2 + (1/2)</gadget>
<output>5/2 = around 2.5</output>

<gadget id="calculator">20 / (5/2)</gadget>
<output>8</output>

<gadget id="calculator">8 * (1/2)</gadget>
<output>4</output>

<result>4</result>