This is a numerical logical reasoning problem, and the key to solving the problem is to sort out the information of each guess, and gradually eliminate and determine the number.

It is known that the teacher wrote four non-repeating numbers, and Xiao Ming's feedback from four guesses is as follows:

1st "0529": 0, 5, 2, 9 are excluded → no correct numbers.
The second "1438": 2 numbers are guessed correctly but in the wrong position→ the correct number is in 1, 4, 3, 8 and is not in the corresponding position (1≠ thousand, 4≠100, 3≠ ten, 8≠ single digit).
The third "6187": guess 2 numbers correctly but in the wrong position→ the correct number is in 6, 1, 8, 7 and is not in the corresponding position (6≠ thousand, 1≠100, 8≠ ten, 7≠ single digit).

The fourth 6378: guess 3 numbers correctly, 2 position pairs→ combine the first three times to filter valid information.
Reasoning core
Lock the repeated numbers: the second and third times both contain "8", and the fourth time also has "8", combined with the first elimination, it is determined that "8" is the correct number, and because the second and third "8" are in the wrong position, "8" is not in the single digit or ten digits, but can only be in the thousand or hundred digits.

The article is not finished. Click on the next page to continue.