# Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 1)
1.
Which one of the following is not a prime number?
31
61
71
91
Explanation:
91 is divisible by 7. So, it is not a prime number.
Discussion:
105 comments Page 1 of 11.

Monisha Mohanan said:   3 years ago
@All.

Prime number means that a number that is divisible only by itself and 1

Examples : 2,3,5,7,11.
Now in our question the options s 31, 61,71 and 91 here I think in our example we can find that the prime numbers only start with 2,1,3,5,7.
(44)

Sharma said:   3 years ago
91 prime or not.

Which square number is exceeds 91?

10 ^2 right. So let's take a prime number which is less than 10.
2, 3, 5, 7.

Check the given number is divisible by 2, 3, 5, 7.
If it is divisible then it is not a prime number.
If not that would be a prime number.
(28)

Sindhuja B said:   3 years ago
The Question is "which is not a prime number".

In a very simple way how do we check whether a number is prime or not, .

The number should be divisible by one & the number it self right!.
Now see their options, that are, .

31. - is a prime number which can only be divided 1 & the number itself.
61. - same here.
71. - here too.
91. - is divisible by 1, 7, 91.

So, among other options, 91 is not a prime number.
(25)

Vishala said:   2 years ago
Thank you all for explaining the answer.
(17)

Keshav said:   4 months ago
How to find the prime number?
(16)

Jitu said:   3 years ago
Why only 91 is not a prime number?

In this case, 71 is also divisible by 3.
(9)

Amare muluken said:   1 year ago
Thanks all for explaining the answer.
(8)

Jaanu Jaanu said:   2 years ago
Thanks both of you for the clear explanations. @Hafiz and@ Dilip.
(7)

Nishu said:   2 years ago
@All.

Thank You so much, it was very helpful to me.
(7)

Kakrla mallikarjuna rao said:   1 year ago
I think B is the correct answer.
(7)