There were originally 28 passengers in a bus. When it arrived at Youth Station, some got off, and then 12 people got on. At this time, there were 31 passengers on the bus. How many people got off at Youth Station? (solution with equation)
一辆客车原有乘客28名，到了青年站，下了一些，又上来12人，这时车上的乘客是31人，青年站下了多少人？(用方程解答)
<gadget id="calculator">12 - 31</gadget>
<output>-19</output>

<gadget id="calculator">28 + (-19)</gadget>
<output>9</output>

<result>9</result>