# Aptitude - Numbers - Discussion

Discussion Forum : Numbers - General Questions (Q.No. 1)

1.

Which one of the following is not a prime number?

Answer: Option

Explanation:

91 is divisible by 7. So, it is not a prime number.

Discussion:

105 comments Page 2 of 11.
Vengala rao said:
1 decade ago

Hai, santhosh your explanation is very nice.

Santhosh said:
1 decade ago

How you will consider 7 when you are checking for 31?

Karthick said:
1 decade ago

Thank you santhose:) your idea is too good to identify the prime no.

Yogendra said:
1 decade ago

Thanks santosh very much

Manali said:
1 decade ago

Thank you santosh.

R.DEIVASIGAMANI said:
1 decade ago

How to identify prime number and not prime number by easy method?

Santosh(pydah) said:
1 decade ago

91 is divided by 7 thats why it is not prime number.

Shekhar said:
1 decade ago

The number which is only divisible by itself and by 1, is called a prime number.

Dilipkumar(cse) said:
1 decade ago

First you memorize these below numbers,

2, 3, 5, 7.

1--1379.

2--39.

3--17.

4--137.

5--39.

6--17.

7--139.

8--39.

9--7.

These are the shortcuts for prime number. Lets see, 1--1379 means 11 is prime, 13 is prime, 17 is prime, 19 is prime. Likewise 2--39 means 23 is prime, 29 is prime. This is the easy way to memorize the prime number. Its very easy (just you have to memorize the above given no).

2, 3, 5, 7.

1--1379.

2--39.

3--17.

4--137.

5--39.

6--17.

7--139.

8--39.

9--7.

These are the shortcuts for prime number. Lets see, 1--1379 means 11 is prime, 13 is prime, 17 is prime, 19 is prime. Likewise 2--39 means 23 is prime, 29 is prime. This is the easy way to memorize the prime number. Its very easy (just you have to memorize the above given no).

Gomathi said:
1 decade ago

Thank you santhosh. And explain with one or more examples please.

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