Prime Number Quiz

Which of the following numbers is prime?

• 323

• 571

• 513

• 715

Answer explanation

A prime number is only divisible by 1 and itself. 571 is prime as it has no divisors other than 1 and 571. The other numbers (323, 513, 715) can be divided by numbers other than 1 and themselves.

Find the smallest three digit prime number?

• 107

• 109

• 103

• 101

Answer explanation

The smallest three-digit prime number is 101. It is the first prime number that has three digits, as 100 is not prime (divisible by 2 and 5). The other options, 103, 107, and 109, are larger than 101.

Which of the following pairs of numbers are co-prime?

• 28, 81

• 12, 27

• 21, 56

• 36, 20

Answer explanation

The numbers 28 and 81 are co-prime because they have no common factors other than 1. In contrast, the other pairs share common factors, making them not co-prime.

One-third of the sum of all the prime numbers greater than 5 but less than 18 is the square of:

• 3

• 5

• 6

• 4

Answer explanation

The prime numbers greater than 5 and less than 18 are 7, 11, 13, 17. Their sum is 48. One-third of 48 is 16, which is the square of 4. Thus, the correct answer is 4.

Which of the following is a prime number?

• 143

• 173

• 123

• 213

Answer explanation

A prime number is only divisible by 1 and itself. Among the choices, 173 is prime as it has no divisors other than 1 and 173. The other numbers (143, 123, 213) can be divided by numbers other than 1 and themselves.

Find the sum of prime no. between 50 and 60.

• 118

• 114

• 110

• 112

Answer explanation

The prime numbers between 50 and 60 are 53, 59. Their sum is 53 + 59 = 112, which is the correct answer.

Find the number of all prime numbers less than 55.

• 18

• 17

• 16

• 15

Answer explanation

The prime numbers less than 55 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, 47, 53. Counting these gives a total of 16 prime numbers, making the correct answer 16.

The number of pairs of twin primes between 1 and 100 are:

• 7

• 8

• 10

• 9

Answer explanation

Twin primes are pairs of primes that differ by 2. The pairs between 1 and 100 are (3, 5), (5, 7), (11, 13), (17, 19), (29, 31), (41, 43), (59, 61), and (71, 73). Thus, there are 8 pairs of twin primes.

The number that has factors other than 1 and itself is called a ............. number.

• Prime Number

• Composite Number

• Even Number

• Odd Number

Answer explanation

A composite number is defined as a number that has factors other than 1 and itself. In contrast, a prime number has exactly two distinct factors: 1 and itself. Therefore, the correct answer is composite number.

Find the number of prime number less than 20.

• 9

• 7

• 10

• 8

Answer explanation

The prime numbers less than 20 are 2, 3, 5, 7, 11, 13, 17, and 19. Counting these gives a total of 8 prime numbers, making the correct answer 8.