There are 1000 students in the school who can dance or sing, 750 of them can sing, 200 can sing and dance, so how many people can dance?
全校有1000学生会跳舞或唱歌，其中会唱歌的750人，既会唱歌又会跳舞的200人，那么会跳舞的为多少人．
<gadget id="calculator">750 - 200</gadget>
<output>550</output>

<gadget id="calculator">1_000 - 550</gadget>
<output>450</output>

<result>450</result>