Divisibility Rule
A positive integer N is Divisible by,
2: if the last digit of N is 2, 4, 6, 8, or 0;
3: if the sum of digits of N is a multiple of 3;
4: if the last 2 digits of N are a multiple of 4;
5: if the last digit of N is either 0 or 5;
6: if N is divisible by both 2 and 3;
7: if subtracting twice the last digit of N from the remaining digits gives a multiple of 7
(e.g 658 = 65 - 2 x 8 = 65 - 16 = 49, which is a multiple of 7)
8: if the last 3 digits of N are a multiple of 8;
9: if the sum of digits of N is a multiple of 9;
10: if the last digit of N is 0;
11: if the difference of the alternating sum of digits of N is a multiple of 11
(e.g. 510510 = (5 + 0 + 1) - (1 + 5 + 0) = 6 - 6 = 0, So this is divisible by 11)
12: if N is divisible by both 3 and 4.
For more informations about Divisibility rules, please check, Wikipedia
Unit Digit
Unity means one, so the units digit is the digit in the one's column.
(e.g for the number 168, 8 is the unit digit)
To find out the unit digit in the product of the numbers, only consider the unit digit in each numbers
e.g. 753 x 43 x 1236 x 864
unit digit in each numbers
3 x 3 x 6 x 4 = 216, So 6 is the unit digit.
