21 isn't because 7*3=21.
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From 10 to 30, there are 21 numbers.Six of them are prime numbers: 11, 13, 17, 19, 23, and 29.If you pick a number at random from 10 to 30, the probabilitythat it's a prime number is6/21 = 2/7 = 28.57% (rounded)
3 x 3 = 9 (Not a prime ; Composite) 1 x 19 = 19 ( Prime) 3 x 7 = 21 (Note a prime: Composite) 5 x 5 = 25 (Not a prime ; Composite).
2 3 5 7 11 13 17 19.
13 is prime so it is not the number. 15 is the product of 3 and 5, two prime numbers, so it fits the conditions. 17 is prime so it is not the number. 19 is prime so it is not the number. 15 is the only odd number between 11 and 21 that fits the conditions. However, if 21 is included in the range, it also is the product of two prime numbers: 3 x 7.
To solve this problem, we first identify the prime numbers between 1 and 24, which are 2, 3, 5, 7, 11, 13, 17, 19, and 23. Next, we pair the numbers such that the sum of each pair is a prime number. One possible solution is: (1, 23), (2, 11), (3, 7), (5, 19), (13, 11), (17, 7). This pairing satisfies the conditions given in the question.