The following is said to be a question in the entry exam of an elementary school in Beijing.
Given nine integers 1 through 9, we can groups them as follows:
1, 3, 5, 7, 9
2, 4, 6, 8
Clearly, they are grouped according to odd and even numbers. Now, the question is, according to which rule are they grouped into three groups as follows?
1, 3, 7, 8
2, 4, 6
Hint: You must be able to speak Mandarin Chinese in order to solve the problem. To be honest, I didn’t come up to this answer. So, I think it is necessary to give this hint.
Source: Scientist Wu Baojun (吴宝俊) of the Chinese Academy of Science (中国科学院). According to Dr. Wu, none of the dozens of PhDs in his office could answer the question. The answer is that they are grouped according to the their pronunciation tones (first, third and fourth) in Mandarin Chinese.