If it is divisible by 36, it is also divisible by 4, meaning the last two digits, 5B, must be divisible by 4 (B is 2 or 6).I am having problems with these ones:

The 4-digit number A 55 B is divisible by 36. What is the sum of A & B.

Also if it is divisible by 36, it is also divisible by 9, so A+5+5+B is divisible by 9, so A+B must be either 8 or 17.

Since B is at most 6, it is impossible for A+B to equal 17, so the sum must be 8.

Of 3 numbers, two are 1/2 and 1/3. What should the third number be so that the average of all three is 1?

You're welcome, though there is a button for that type of thing (hint, hint...)Thank you!