# FAQ: Methods, Blocks, & Sorting - Why Methods?

This community-built FAQ covers the “Why Methods?” exercise from the lesson “Methods, Blocks, & Sorting”.

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for i in 2…n-1
if n % i == 0
is_prime = false
end

please can someone be so kind to explain what is it?

In the example code, we’re checking whether `n` is an integer, and then whether it is a prime number or not. Prime numbers can only be divided by themselves and 1.

In the portion of the code you mentioned, `i` is the iterator in the `for` loop, which is checking one at a time whether `n` is divisible by a number between 2 and `n-1`.

`n` represents the integer we’re checking, and `n-1` is one less than the integer.

For example, `prime(11)` results in a `for` loop that iterates from 2 to 10. Since 11 is not divisible by any of these numbers, `n % i` is never `== 0`; it is a prime number.

`prime(51)` results in a `for` loop that iterates from 2 to 50. Since 51 is divisible by some numbers in this range, it is not a prime number. This is checked with `n % i == 0` For example, `51 % 3 == 0`. So `is_prime = false` in the case of 51.

Thank you, Marilyn! It is much better now.

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