Prime Numbers Quiz

Find the total number of prime numbers less than 50.

• 13

• 15

• 17

• 14

Answer explanation

The prime numbers less than 50 are: 2, 3, 5, 7, 11, 13, 17, 19, 23, 29, 31, 37, 41, 43, and 47. Counting these gives a total of 15 prime numbers, making the correct answer 15.

What is the positive difference between the sum of all prime numbers between 11 and 20 (both included) and the sum of all prime numbers between 30 and 50 (both included)?

• 139

• 141

• 137

• 135

Answer explanation

The prime numbers between 11 and 20 are 11, 13, 17, 19, summing to 60. The prime numbers between 30 and 50 are 31, 37, 41, 43, 47, summing to 199. The positive difference is 199 - 60 = 139, which is the correct answer.

The greatest prime number less than 200 is:

• 199

• 193

• 197

• 191

Answer explanation

The greatest prime number less than 200 is 199. It is the largest number in the list of prime numbers below 200, which includes 191, 193, and 197, all of which are smaller than 199.

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.

Which of the following pairs is NOT a pair of twin primes?

• 11, 13

• 71, 73

• 131, 133

• 191, 193

Answer explanation

Twin primes are pairs of primes that differ by 2. The pair 131, 133 is not valid because 133 is not a prime number (it is divisible by 7). The other pairs listed are all twin primes.

Which of the following is the prime number series from 1 to 20?

• 3, 5, 7, 11, 13, 17, 19

• 2, 5, 7, 9, 11, 13, 17, 19

• 2, 3, 5, 7, 11, 13, 17, 19

• 1, 2, 3, 5, 7, 11, 13, 17, 19

Answer explanation

The correct series of prime numbers from 1 to 20 is 2, 3, 5, 7, 11, 13, 17, 19. This series includes all prime numbers, while the other options either omit 2 or include non-prime numbers like 9.

Calculate the difference between the largest and the smallest two-digit prime number.

• 82

• 83

• 84

• 86

Answer explanation

The smallest two-digit prime number is 11 and the largest is 97. The difference is 97 - 11 = 86, which is the correct answer.

Which of the following number is not composite?

• 209

• 203

• 161

• 109

Answer explanation

A composite number has more than two distinct positive divisors. The number 109 is prime, having only two divisors: 1 and 109. In contrast, 209, 203, and 161 are composite numbers.