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

Prime numbers are those that cannot be divided by another number (other than themselves and 1). In other words, prime numbers have factors of themselves and 1.

For example, 3 is a prime number because its only factors are 3 and 1.

6 is not a prime number because it can be factored to 3*2.

Therefore, the correct answer is c. 3,11,23,31

Prime numbers can only be divided by 1 and itself.

First group: - It contains 15, and 15 can be divided by 3 and 5 to get a whole number.

Second group: - 49 can be divided by 7 to receive 7. So this is wrong.

Third group: - This group can be considered all prime numbers, so this is correct.

Fourth group: - Incorrect. Because 9/3 = 3

Answer: - c. 3,11,23,31 are all prime numbers.