Some More Divisibility Rules
(i)    If a number is divisible by another number then it is divisible by each of the factors of that number.
         Ex.    18 is divisible by 9.  The factors of 9 is 3. 18 is also divisbile by 3.
(ii)    If a number is divisible by two co-prime numbers then it is divisible by their product also.
       Ex.    The number 80 is divisible by 4 and 5. It is also divisible by 4 × 5 = 20, and 4 and 5 are 
co-primes.
 Similarly, 60 is divisible by 3 and 5 which are co-primes. 60 is also divisible by 3 × 5 = 15.
(iii)     If two given numbers are divisible by a number, then their sum is also divisible by that number.
       Ex.    The numbers 16 and 20 are both divisible by 4. The number 16 + 20 = 36 is also divisible by 4. 
(iv)     If two given numbers are divisible by a number, then their difference is also divisible by that number.
      Ex.    The numbers 35 and 20 are both divisible by 5. Is their difference 35 – 20 = 15 also divisible by 5.