Is 775 a prime number or a composite number?

Answer 1

If we can find one factor, besides '1' and the number itself, then the number is not prime.
There may be more factors, but all we need is one in order to prove it 'not prime'.

Looking at '775', we notice that it ends in '5'. This tells us that it's a multiple of '5'; in other words,
'5' is a 'factor' of 775.

That's all it takes. 775 is composite, not prime.