Which of the following groups of numbers are all prime numbers?
(a) 2, 5, 15, 19  (b) 3, 11, 23, 31 (c) 2, 3, 5, 9 (d) 7, 17, 29, 49

Solution:

Prime numbers are the numbers that have only two factors, that are, 1 and the number itself.

Let us examine each group:

• 2, 5, 15, 19 ------> 2, 5, 19 are prime but 15 = 3 × 5 is composite
• 3, 11, 23, 31 ------> all are prime numbers
• 2, 3, 5, 9 --------> 2, 3, 5 are primes but 9 = 3 × 3 is composite.
• 7, 17, 29, 49 --------> 7, 17, 29 are primes but 49 = 7 × 7 is composite.

Thus, option (b) 3, 11, 23, 31 is the group containing all the prime numbers.

Which of the following groups of numbers are all prime numbers?
(a) 2, 5, 15, 19  (b) 3, 11, 23, 31 (c) 2, 3, 5, 9 (d) 7, 17, 29, 49

Summary:

Option (b) 3, 11, 23, 31 is the group containing all the prime numbers.