-3
Without repeats there are 4 × 3 = 12 possible 2 digit numbers. With repeats there are 4 × 4 = 16 possible 2 digit numbers.
9 x 9 x 8 x 7 = 4,536
There are 8*9*8*7*6*5*4 = 483840 numbers.
7777
-3
-3
There are 840 4-digit combinations without repeating any digit in the combinations.
Without repeats there are 4 × 3 = 12 possible 2 digit numbers. With repeats there are 4 × 4 = 16 possible 2 digit numbers.
9 x 9 x 8 x 7 = 4,536
9 x 9 x 8 x 7 = 4,536
9 x 9 x 8 x 7 = 4,536
You can make 4*3*2/2 = 12 numbers.
There are 8*9*8*7*6*5*4 = 483840 numbers.
7777
25
24