Originally there were 50 people on the bus. After arriving at the station, some people got off and then 13 people got on. At this time, there were 39 people on the bus. How many people went down?
汽车上原来有50人，到站后下去一些人后又上来13人，这时车上共有39人，问下去多少人？
<gadget id="calculator">13 - 39</gadget>
<output>-26</output>

<gadget id="calculator">50 + (-26)</gadget>
<output>24</output>

<result>24</result>