| How do you know if a number is divisible by 3? | sum of digits divisible by 3 |
| how do you know if a number is divisble by four | last two digits are div by 4 |
| how do you know if a number is divisible by six | even and divisble by three |
| how do you know if a number is divisbile by 9 | sum of digits are divisible by 9 |
| what is the work formula | (x*y)/(x+y) |