Deric D. answered • 02/02/16

Professional, Analytical and Creative Thinker Specializing in Math

Hi Alexis.

First determine how many numbers exist in the range:

Answer = 899 - 20 = 879 (900 and 20 are not available).

First lets work on the 2 digit numbers:

From the set you have for the first and second digit of the number.

Non-Repeat = 6, 5

Repeating = 6, 6

Total Combinations for 21-99

Non-Repeat = 30

Repeating = 36

Repeating = 36

Now for the 100 - 899 range

Digit counts assignments: (here the 9 can't be used as the first digit)

Non-Repeat = 5, 5, 4

Repeating = 5,6,6

Repeating = 5,6,6

Total Combinations for the 100 - 899 range

Non-Repeat = 100

Repeating = 180

Total combination for 21-899

Non-Repeat = 130

Repeating = 216

Non-Repeat = 130

Repeating = 216