The rule to decide if a number is divisible by 9 is to look at the sum of the digits. If the sum of the digits is divisible by 9, then so is the number.
if the number is divisible by 2 and 3 then it is divisible by 6 =D
To find out if a number is divisible by 8 the number must be divisible by 2 and 4!
Just carry out the division, and see if you get an integer. It isn't worth the trouble to memorize or, worse, figure out divisibility rules for all sorts of large numbers.
A number is divisible by 15 if it is divisible by 5, and by 3. For example, 165 is divisible by 15, since it ends in 5, and the sum of its digits is divisible by 3.
No - because it's an odd number !
The only number by which four is divisible is two.
In most cases, it is easier to do the division than to use some special divisibility rule. Divisibility rules only save you time in some special cases, such as:2, 4, 8, 5, 10, 25 (look at the last digit or digits)3, 9 (add the digits, and see if it is divisible by 3 or by 9, respectively)7, 11, and 13 (separate the last three digits and subtract from the remaining number)
If the sum of the digits is a multiple of 3, yhen the number is divisible by 3.