数学题：一些小朋友排成一队，从前往后数小明排在第７位，从后往前数小明排在第９位。这队一共有多少人？

7+9-1＝15（人）

思考：为什么减1？

提高题：一些小朋友排成一队，从前往后数小明和小刚分别排在第7位和第8位，从后往前数他们分别排在第10位和第11位。这队一共有多少？

思考：条件变多了，变复杂了，怎么算？

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