Number combinations!?

Question

ok...

what are all the number combinations that are 4-8 digits. with the number 0,1,2,3,4,5,6,7,8???

Answer 1

Four digits:

8 choices for the first digit (assuming that a leading 0 is not allowed)

9 choices for the second digit (no nine)

9 choices for the third digit (no nine)

9 choices for the fourth digit (no nine)

8 x 9 x 9 x 9 = 5,832 combinations

Five digits:

8 x 9 x 9 x 9 x 9 = 52,488 combinations

Six digits:

8 x 9 x 9 x 9 x 9 x 9 = 472,392 combinations

Seven digits:

8 x 9 x 9 x 9 x 9 x 9 x 9 = 4,251,528 combinations

Eight digits

8 x 9 x 9 x 9 x 9 x 9 x 9 = 38,263,752 combinations

Combinations of 4-8 digits:

5,832 + 52,488 + 472,392 + 4,251,528 + 38,263,752

= 43,045,992 combinations

P.S.  Don't you dare ask me to list them all!  :-D

Answer 2

Assuming the first digit isn't a zero...

8(9^3)+8(9^4)+8(9^5)+8(9^6)+8(9^7)

=8(9^3+9^4+9^5+9^6+9^7)

=8(5380749)

=43045992 possible combinations