Aptitude - Numbers - Discussion

A negative number can be a prime number?

Which number is only divisible by 1 and the same number is called prime number.

@KARTHIK.

If number is 97.

9-(2*7) = is not positive number.

Number is 91.
Take out last 1 and multiply by 2.

9 - (1*2) = 9 - 2 = 7.
So it is divisible by 7.

If we have more digits repeat the process.
It is easy.

Prime number means, the number which is non actionable.

Hi,

11>square root of(91).
(11*11=121 =>11^2 > square root of (91)).

Then prime numbers below 11 are 2, 3, 5, 7

So 91 is divisible by 7.
Hence 91 is not a prime number.

Prime number is defined as divisible by "itself" and by "one" only.

The simple way is we should know tables to find which is a prime number.

Simple meaning of prime no-"The number which is only divisible by itself and by 1, is called a prime number".

If any given number is prime or not, how can u find out? here is one way to solve for that one.

Step 1:

Find the square root for given number. if it is not a perfect square take nearest number of that on.

Ex: 91 is given. 8 is nearest square root (81) [91<x^2]

Step 2:

Write all prime numbers below that square root number.

2 3 5 7

Step 3:

If the given number(91) is not divisible with any one of the above numbers(2 3 5 7) then that number is prime number otherwise it's not.