Read the number from left to right and add the digits in alternation. Check if the difference between the sum of its alternate digits is divisible by 11 If so, the original number is also divisible by 11. In 2728, for example, the sum of the digits is alternately 2 - 7 + 2 - 8, which is -11. -11 and 2728 are both divisible by 11, thus.