2.25: pay attention to pennies and dimes.  When you get to "2" and "4", it is incorrect.  Think about their parities (even or odd).

2.26: The operations won't change the total sum mod 3.

2.22: Each digit appear in each place the same number of times, except when 0 is the leading digit.

2.30: Similar to 2.26, consider mod 3.

2.32: for any two integers, their sum and difference have the same parity.