My computer says there are 3584 [Thanks geno3141 - I only counted the first 3000!!!] 4-digit numbers that have no 1 or 2 in them. In other words, they must start with:
3000 3003 3004 3005 3006 3007 3008 3009 3033 3034.......etc. and end with ..... 9993 9994 9995 9996 9997 9998 9999 Total = 3584 such numbers.
+23252 There are 7 choices for the first digit: 3, 4, 5, 6, 7, 8, and 9; only 0, 1, and 2 are not acceptable.
After the first digit, there are 8 choices for the second, third, and fourth digits (only 1 and 2 are not acceptable).
This means that there are 7 x 8 x 8 x 8 = 3584 possibilities.
