After the closing ceremony of the sports meeting, everyone was about to leave. The monitor Xiaoyue asked the whole class to stand in a line and count the number of people (she was not in the team herself). She counted from left to right first, and found that Dongdong was the 25th; then she counted from right to left, and found that Archie was exactly 29th. If there are 31 people in the team, then the difference between Dongdong and Archie How many people are there?
运动会闭幕式结束后，大家准备散场，班长小悦让全班同学站成一行清点人数(她自己并不在队伍中)．她先从左往右数，发现冬冬是第25个；然后她又从右往左数，发现阿奇正好是第29个，如果队伍里一共有31个，那么冬冬和阿奇之间有几个人？
<gadget id="calculator">29 - 31 - 2</gadget>
<output>-4</output>

<gadget id="calculator">25 + (-4)</gadget>
<output>21</output>

<result>21</result>