# 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:
101 comments Page 1 of 11.

Vishala said:   2 months ago
Thank you all for explaining the answer.
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Nishu said:   4 months ago
@All.

Thank You so much, it was very helpful to me.
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Jaanu Jaanu said:   9 months ago
Thanks both of you for the clear explanations. @Hafiz and@ Dilip.
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Monisha Mohanan said:   2 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.
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Jitu said:   2 years ago
Why only 91 is not a prime number?

In this case, 71 is also divisible by 3.
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Sharma said:   2 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.

Sindhuja B said:   2 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.
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Tharun said:   2 years ago
91 is correct because the prime number is one which is having two distinct factors so, that 91 having more than two factors.

Harika said:   2 years ago
31 is the prime number.

Pooja said:   2 years ago
n*n>=p in this form, how take that value by comparing p? Please explain anyone.