Because they have more than two factors.
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∙ 7y ago21, 51, 81, 91.
51 is composite.
51 composite, 61 prime.
51 is composite.
91 is the only composite factor of 91. 7 and 13 are prime.
41 is prime. 51 is composite. 51=3 x 17 . 71 is prime. 81 is composite. 92 91 is composite. 91 = 7 × 13
both are composite numbers 51 is divisible by 1,3,17,51 and 91 by 1,7,13,91
6, 9, 15, 28, 51, and 91.
61 and 71 are prime numbers the rest are composite numbers
21, 51, 81, 91.
21 is divisible by 3 and 7, so it is composite. 91 is divisible by 7 and 13, so it is composite. 51 is divisible by 3 and 17. 31 is divisible by only 1 and itself, so it is the prime number.
3 x 17 = 51. It has factors other than 1 and itself. It is composite. 61 is prime. Its only factors are 1 and 61. 71 is prime. Its only factors are 1 and 71. 7 x 13 = 91. It is a composite number.
51 is composite.
91 is a Composite Number.
91 is a composite number. This is because composite numbers are any number that has another factor besides one and itself. Therefore, since 7 and 13 are factors of 91 that makes it a composite number.
51 is composite. Becasuse 17 x 3 = 51 It is two prime numbers multiplied together to make a composite.
91 is composite.