27个。如果单从数学角度看，这个问题是可以计算的。即３人３天共吃了３个西瓜，即９个人３天会吃掉９个西瓜。则，９天，９个人，可以吃掉２７个西瓜。

27. From a mathematical point of view, this problem can be calculated. That is, three people ate three watermelons in three days, that is, nine people would eat nine watermelons in three days. Then, 9 people can eat 27 watermelons in 9 days.

三个人三天吃三个西瓜，九个人九天吃二十七个西瓜。

Three people eat three watermelons in three days, and nine people eat twenty-seven watermelons in nine days.

1、如果单从数学角度看，这个问题是可以计算的。即３人３天共吃了３个西瓜，即９个人３天会吃掉９个西瓜。９天，为３天的３倍，则，９天，９个人，可以吃掉２７个西瓜。

1. From a mathematical point of view, this problem can be calculated. That is, three people ate three watermelons in three days, that is, nine people would eat nine watermelons in three days. Nine days, three times as many as three days, and nine people can eat 27 watermelons in nine days.

2、但在实际生活中，此类事件是可以随意变更的，九个人九天可能吃的数比二十七个多，也有可能比二十七个少，是没有确切答案的。

2. But in real life, such events can be changed at will. Nine people may eat more or less than twenty-seven in nine days. There is no exact answer.