The number 10 has four factors:1, 2, 5 and 10. The table below lists the number of factors for some numbers.

Number
Number of factors
21
4
23
2
25
3
27
4
29
2

From this, we can say that the number of prime numbers between 20 and 30 is

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answer is B.

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Detailed Solution

Concept: First, we know that numbers with only two divisors are prime numbers. Unsynthesized numbers are sometimes called prime numbers. Therefore, find a prime number from 21 to 30, that is, a number with only two divisors.
We know that prime numbers are numbers that are divisible by themselves and only one, and that the set of prime numbers is

increase.
Currently, the prime numbers from 20 to 30 are 23 to 29.
Therefore, the number of prime numbers from 20 to 30 is 2.
Hence, the correct answer is option 2.

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