Question

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

• A. $0$
• B. 22
• C. $3$
• D. $4$

Answer 1

The correct option is B 22

We know that a prime number is a number that is divisible only by itself and $1$ and the set of prime numbers is $2,3,5,7,11,13,17,19,23,29,\mathrm{31.....}$
Now, the prime numbers between $20$ and $30$ are $23$ and $29$

Hence, the number of prime numbers between $20$ and $30$ is $2$.