The composite numbers encircled are: 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 26, 27, 28, 30, 32, 33, 34, 35, 36, 38, 39, 40, 42, 44, 45, 46, 48, 49, 50, 51, 52, 54, 55, 56, 57, 58, 60, 62, 63, 64, 65, 66, 68, 69, 70, 72, 74, 75, 76, 77, 78, 80, 81, 82, 84, 85, 86, 87, 88, 90, 91, 92, 93, 94, 95, 96, 98, and 99.
A composite number is a positive integer that has at least one divisor other than 1 and itself. In other words, it can be formed by multiplying two smaller positive integers.
Here's a breakdown of why each number in the list is composite:
- 4: 2 x 2
- 6: 2 x 3
- 8: 2 x 4
- 9: 3 x 3
- 10: 2 x 5
- 12: 2 x 6, 3 x 4
- 14: 2 x 7
- 15: 3 x 5
- 16: 2 x 8, 4 x 4
- 18: 2 x 9, 3 x 6
- 20: 2 x 10, 4 x 5
- 21: 3 x 7
- 22: 2 x 11
- 24: 2 x 12, 3 x 8, 4 x 6
- 25: 5 x 5
- 26: 2 x 13
- 27: 3 x 9
- 28: 2 x 14, 4 x 7
- 30: 2 x 15, 3 x 10, 5 x 6
- 32: 2 x 16, 4 x 8
- 33: 3 x 11
- 34: 2 x 17
- 35: 5 x 7
- 36: 2 x 18, 3 x 12, 4 x 9, 6 x 6
- 38: 2 x 19
- 39: 3 x 13
- 40: 2 x 20, 4 x 10, 5 x 8
- 42: 2 x 21, 3 x 14, 6 x 7
- 44: 2 x 22, 4 x 11
- 45: 3 x 15, 5 x 9
- 46: 2 x 23
- 48: 2 x 24, 3 x 16, 4 x 12, 6 x 8
- 49: 7 x 7
- 50: 2 x 25, 5 x 10
- 51: 3 x 17
- 52: 2 x 26, 4 x 13
- 54: 2 x 27, 3 x 18, 6 x 9
- 55: 5 x 11
- 56: 2 x 28, 4 x 14, 7 x 8
- 57: 3 x 19
- 58: 2 x 29
- 60: 2 x 30, 3 x 20, 4 x 15, 5 x 12, 6 x 10
- 62: 2 x 31
- 63: 3 x 21, 7 x 9
- 64: 2 x 32, 4 x 16, 8 x 8
- 65: 5 x 13
- 66: 2 x 33, 3 x 22, 6 x 11
- 68: 2 x 34, 4 x 17
- 69: 3 x 23
- 70: 2 x 35, 5 x 14, 7 x 10
- 72: 2 x 36, 3 x 24, 4 x 18, 6 x 12, 8 x 9
- 74: 2 x 37
- 75: 3 x 25, 5 x 15
- 76: 2 x 38, 4 x 19
- 77: 7 x 11
- 78: 2 x 39, 3 x 26, 6 x 13
- 80: 2 x 40, 4 x 20, 5 x 16, 8 x 10
- 81: 3 x 27, 9 x 9
- 82: 2 x 41
- 84: 2 x 42, 3 x 28, 4 x 21, 6 x 14, 7 x 12
- 85: 5 x 17
- 86: 2 x 43
- 87: 3 x 29
- 88: 2 x 44, 4 x 22, 8 x 11
- 90: 2 x 45, 3 x 30, 5 x 18, 6 x 15, 9 x 10
- 91: 7 x 13
- 92: 2 x 46, 4 x 23
- 93: 3 x 31
- 94: 2 x 47
- 95: 5 x 19
- 96: 2 x 48, 3 x 32, 4 x 24, 6 x 16, 8 x 12
- 98: 2 x 49, 7 x 14
- 99: 3 x 33, 9 x 11
