Question: How many prime numbers are there between 1 and 20?
Options:
8
9
10
11
Correct Answer: 9
Solution:
There are 8 prime numbers between 1 and 20: 2, 3, 5, 7, 11, 13, 17, 19.
How many prime numbers are there between 1 and 20?
Practice Questions
Q1
How many prime numbers are there between 1 and 20?
8
9
10
11
Questions & Step-by-Step Solutions
How many prime numbers are there between 1 and 20?
Step 1: Understand what a prime number is. A prime number is a number greater than 1 that has no positive divisors other than 1 and itself.
Step 2: List the numbers between 1 and 20. The numbers are: 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20.
Step 3: Check each number in the list to see if it is prime.
Step 4: The number 2 is prime (divisors: 1, 2).
Step 5: The number 3 is prime (divisors: 1, 3).
Step 6: The number 4 is not prime (divisors: 1, 2, 4).
Step 7: The number 5 is prime (divisors: 1, 5).
Step 8: The number 6 is not prime (divisors: 1, 2, 3, 6).
Step 9: The number 7 is prime (divisors: 1, 7).
Step 10: The number 8 is not prime (divisors: 1, 2, 4, 8).
Step 11: The number 9 is not prime (divisors: 1, 3, 9).
Step 12: The number 10 is not prime (divisors: 1, 2, 5, 10).
Step 13: The number 11 is prime (divisors: 1, 11).
Step 14: The number 12 is not prime (divisors: 1, 2, 3, 4, 6, 12).
Step 15: The number 13 is prime (divisors: 1, 13).
Step 16: The number 14 is not prime (divisors: 1, 2, 7, 14).
Step 17: The number 15 is not prime (divisors: 1, 3, 5, 15).
Step 18: The number 16 is not prime (divisors: 1, 2, 4, 8, 16).
Step 19: The number 17 is prime (divisors: 1, 17).
Step 20: The number 18 is not prime (divisors: 1, 2, 3, 6, 9, 18).
Step 21: The number 19 is prime (divisors: 1, 19).
Step 22: Count the prime numbers found: 2, 3, 5, 7, 11, 13, 17, 19. There are 8 prime numbers.
Prime Numbers – A prime number is a natural number greater than 1 that cannot be formed by multiplying two smaller natural numbers. It has exactly two distinct positive divisors: 1 and itself.
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