Divisibility Rules You Need to Know

Shortcuts for Factoring

You don't always need a calculator to know if a number divides evenly into another. These divisibility rules can save you immense time.

The Essential Rules

• Rule for 2: The last digit is even (0, 2, 4, 6, 8).
• Rule for 3: The sum of the digits is divisible by 3. (e.g., 123 -> 1+2+3=6. Yes!)
• Rule for 4: The last two digits form a number divisible by 4.
• Rule for 5: The last digit is 0 or 5.
• Rule for 6: The number passes the rules for both 2 and 3.
• Rule for 9: The sum of the digits is divisible by 9.
• Rule for 10: The last digit is 0.

Advanced Rules

• Rule for 8: The last three digits form a number divisible by 8.
• Rule for 11: Subtract the last digit from the remaining number. If the result is divisible by 11 (or 0), the original number is too. (Alternatively, alternate adding and subtracting digits).