Free Puzzles

I published some free numerical items here, I believe in this way you can know why it is so easy to get a solution which is not right.

Questions:

1) 76, ?, 90, 81, 72, 63, 54, 45, 36, 27, 18, 9

2) 8127, 2187, 1827, ?

3) 84, 36, 24, 12, ?

4) 24, 16, 12, 4, ?

5) 17, 24, 18, 27, ?

6) 16, 24, 32, 24, ?

7) 52, 25, 32, ?

8) 88, 64, 48, 32, 24, ?