Explain why numbers with a 5 in the ones place are not prime numbers.

Because it's divisible by 5 even though 5 is a prime number

In order for a number to be a prime number, it must only be divisible by 1 and itself. Just like any number that is even can be divisible by 2, any number that ends in 0 or 5 can be divisible by 5. So that is why a number that ends in 5 is not prime, because it has another factor other than 1 and itself, and that would be 5. Hope this helped! :D