✅ A number is divisible by 4 if the last two digits form a number divisible by 4.
| Number | Last Two Digits | Divisible by 4? | Reason |
|---|---|---|---|
| 124 | 24 | ✅ Yes | 24 ÷ 4 = 6 |
| 316 | 16 | ✅ Yes | 16 ÷ 4 = 4 |
| 157 | 57 | ❌ No | 57 ÷ 4 = 14.25 |
| 200 | 00 | ✅ Yes | 0 is divisible by 4 |
| 718 | 18 | ❌ No | 18 ÷ 4 = 4.5 |
✅ A number is divisible by 3 if the sum of its digits is divisible by 3.
| Number | Sum of Digits | Divisible by 3? | Reason |
|---|---|---|---|
| 123 | 1 + 2 + 3 = 6 | ✅ Yes | 6 is divisible by 3 |
| 345 | 3 + 4 + 5 = 12 | ✅ Yes | 12 is divisible by 3 |
| 127 | 1 + 2 + 7 = 10 | ❌ No | 10 is not divisible by 3 |
| 81 | 8 + 1 = 9 | ✅ Yes | 9 is divisible by 3 |
| 100 | 1 + 0 + 0 = 1 | ❌ No | 1 is not divisible by 3 |
✅ A number is divisible by 2 if its last digit is 0, 2, 4, 6 or 8.
| Number | Last Digit | Divisible by 2? | Reason |
|---|---|---|---|
| 12 | 2 | ✅ Yes | Ends in an even digit |
| 57 | 7 | ❌ No | Ends in an odd digit |
| 104 | 4 | ✅ Yes | Ends in an even digit |
| 839 | 9 | ❌ No | Ends in an odd digit |
| 60 | 0 | ✅ Yes | Ends in 0 |
Numbers from 1 and go on: 1, 2, 3, 4, 5, …
Natural numbers plus 0: 0, 1, 2, 3, …
Positive, negative numbers and 0: … -3, -2, -1, 0, 1, 2, …
End with 0, 2, 4, 6, 8: 2, 4, 6, 8, 10, …
End with 1, 3, 5, 7, 9: 1, 3, 5, 7, 9, …
Only 2 factors: 2, 3, 5, 7, 11, …
More than 2 factors: 4, 6, 8, 9, …
Can be written as fractions: 1/2, 3/4, 5/1
Cannot be written as fractions: √2, π
Contain a dot: 3.5, 2.75, …
Old-style: I, V, X, L, C
Fun Facts: 0 is neither positive nor negative. 2 is the only even prime. Numbers go on forever (∞).