Divisibility by 4, 5 and 6

Here's the continuation of divisibility.

Divisibility by 4 can be found out by just looking at the two last digits. Say you have 36764, then you only have to find out if 64 is divisible by 4. If dividing twice by 2 is possible, then 64 is divisible by 4. 64 / 2 = 32. 32 is even and hence can be divided by 2. Therefore 64 is divisible by 4.

Another example: 36786. We need only look at 86. Divide by 2 and get 43. 43 can't be divided by 2, and we conclude that 86, and also 36786 is not divisible by 4.

Divisibility by 5 is as simple as divisibility by 2, only different. All numbers ending with 0 or 5 are divisible by 5.

Divisibility by 6 is tested for by checking divisibility by 2 and checking the result for divisibility by 3. Example 198: It's even and could therefore be divisible by 6. We divide 198 by 2 and get 99. We test if 99 is divisible by 3: 9 + 9 = 18. 18 is divisible by 3. So 99 is divisible by 3. Therefore 198 is divisible by 6. Again, 198 is even. We divided by 2 to get 99 and found 99 to be divisible by 3.