Number Theory Level 25: Rules - digit-sum (3, 9). divisibility rule.
1. Add digits
Use the rule for the selected divisor; do not trial-divide blindly.
Select the digits or multiple required by this divisor.
2. Check multiple of 9
Add digits
Apply the selected rule exactly.
3. Read yes or no
Add digits
Check multiple of 9
Yes
Read the divisibility relation and its semantic answer.