Question

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,

Answer 1

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

Answer 2

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.