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Usage of digit sum:

The number is divisible by 3, when its digit sum is divisible 3.

The number is divisible by 9, when its digit sum is divisible 9.

Instructions:

Digit sum is the sum of all digits of the integer. We write DS(n).

For example: DS(483) = 4 + 8 + 3 = 15.

Example

How much is DS(398)?

Your answer:

DS(398) = ________.

Solution

How much is DS(398)?

Your answer:

DS(398) = 20.

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