Discussion

Explanation:

Let the four-digit number contain digits a, b, c or d.

When we write it in expanded form the digits will have one of these 4 coefficients 1000, 100, 10 or 1.

Now the difference of any two of these coefficients will always be divisible by 9.

Hence, the difference of a 4-digit number and the number formed by permuting its digits would always be divisible by 9.

Hence, option (d).

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