Follow the rule: take the last digit a, the remaining digits b, then compute b − 9a.
Repeat until you get 0 or a two-digit number, then decide if it is a multiple of 13.
Level1
Score0
Streak0
Enter a number and press New Challenge. In Practice mode, you can use hints.
In Challenge mode, hints reduce points.
✅ Enter the next reduced answer in the box and click Submit Step. When you reach final, choose Divisible or Not divisible.
Number
—
Goal: reduce until the answer is 0 or a two-digit number.
Step 1: Multiply the ones digit by 9
Example: ones digit 8 → 8 × 9 = 72
Step 2: Subtract that result from the remaining digits
Example: 345 − 72 = 273
Decision: Is the new answer 0 or a two-digit number?
If NO → restart with the new answer.
Your next answerMode: Practice
Type a number and press New Challenge.
Coach & Steps
Latest first
Tip: When you reach a two-digit number, check if it is one of these multiples of 13:
13, 26, 39, 52, 65, 78, 91.
