Question

show that in any set of 9 positive integers, some of them share all of their primary factors that are less than or equal to 5

Answer 1

The statement is false.

Explanation:

We know that all integer numbers can be written as a product of prime numbers.

For example:

15 = 5*3

15 is a product of two prime numbers, 5 and 3.

28 = 2*2*7

28 is the product of two prime numbers, 2 two times, and 7.

Now, we want to prove that in any set of 9 positive integers, some of them share all of their primary factors that are less than or equal to 5.

Now, let's try to find a counterexample to see if this is false.

The first idea that comes to mind is, what with a set of 9 positive prime numbers?

(2, 3, 5, 7, 11, 13, 17, 19, 23)

So none of these numbers share their primary factors (where the "1" is not considered as a primary factor)

And another counterexample could be:

(2, 3, 5, 7, 11, 13, 17, 6, 10)

Here 6 = 2*3

10 = 2*5

So 6 and 10 share a primary factor (the two) but do not share all of their primary factors that are less than or equal to 5.

So we found two counterexamples of the statement, so we can conclude that the statement is false.