162521

Number 1 is sometimes because it depends what numbers they are even or odd
Number 2 is sometimes because 10 is a multiple of 5 and ends in a 0 but so is 15 and that ends in 5
Number 3 is always because multiples of 10 are multiples of 5 and a multiple of 5 add another multiple of 5 is another multiple of 5 eg: 10+15=25
Number 4 is always because an odd number add an odd number is an even number so it is always
Number 5 is never because odd numbers add odd numbers is even not odd
Number 6 sometimes because you can have decimals which makes the number smaller
Number 7 is never because square numbers are the only numbers that have an odd amount of factors because what a number is is times by itself it counts as one factor.
Number 8 is sometimes because when the numbers are negative numbers are divided by a half they get smaller
Number 9 is sometimes because when the number is negative and you add 5 it can still stay as a negative number.
Number 10 is always because 1 number will already be a multiple of 3 and the other 2 will add will add up to a multiple of 3 and 2 multiples of 3 will add up to make a multiple of 3.