Divisibility Tricks

Test without dividing

An interactive lesson with 6 steps, about 5 minutes: you predict, drag and solve, with instant feedback on every answer. It runs in your browser and needs JavaScript.

What you’ll learn

• 3 and 9: test the digit sum. 2, 5 and 10: test the last digit. 4: test the last two digits.
• 11: take the alternating sum of the digits.
• The tricks work because of how powers of 10 relate to each divisor.

Steps

1. Quick check
2. Why digit sums work
3. Which divide it?
4. The trick for 11
5. Fill in the digit
6. Missing digit