# Visible Divisibility Tests

Visible Divisibility Tests

Most people are familiar with the test for divisibility by 3: add up all the digits and check whether the result (the digit sum) is divisible by 3. Other divisibility tests are less well known, such as alternately adding and subtracting digits to test for divisibility by 11. This Demonstration implements divisibility tests for dividing by 2, 3, …, 11. In all cases the rule is given and a step-by-step application shown, either in "Long" or "Brief" form. The radio buttons choose which test to apply and the slider selects the number to test. (Clicking the "+" sign by the slider opens another panel where numbers can be entered directly or incremented/decremented.)