There are 500 foreign language teachers in a city who know English or German, 375 of them know English, and 100 know both English and German. How many teachers know German?
某市500名外语教师，懂英语或德语，其中懂英语的有375人，既懂英语又懂德语的有100人，那么懂德语的教师有多少人．
<gadget id="calculator">375 - 100</gadget>
<output>275</output>

<gadget id="calculator">500 - 275</gadget>
<output>225</output>

<result>225</result>