5 is but 15 is not a prime number
To find the HCF, you first have to express both numbers as the product of their prime factors: 15 = 3x5 20 = 2x2x5 The next step is to identify any common prime factors. In this case both numbers have a 5 as a prime factor. Therefore the HCF of 15 and 20 is 5.
The prime numbers of 20 are 2, 2 and 5. (2*2*5 = 20)
The product of the prime numbers 3 and 5 is 15.
Prime numbers which are factors of 15: 3&5.
10 and 20 are composite numbers, not prime numbers. The prime factorization of 10 is 2 x 5. The prime factorization of 20 is 2 x 2 x 5.
The prime factors of 15 are: 3, 5
2/5 of the numbers from 1 to 20 are prime numbers
The prime numbers from 1 to 20 are 2, 3, 5, 7, 11, 13, 17, and 19. The original answer incorrectly included 1, 9, and 15.
3*5 = 15 in prime numbers
2, 3, 5, 7, 11, 13, 17, 19 ARE prime numbers! 1, 4, 6, 8, 9, 10, 12, 14, 15, 16, 18, 20 are NOT prime numbers!
5 is prime.