There's a likely typo in rspence's solution for (1)
The corrected version is:
1. Consider the numbers 000 - 999. We want to find the # of integers in this set that do not contain 7's. There are 9 choices (0,1,2,3,4,5,6,8,9) for the first digit, 9 for the second, 9 for the third (two-digit numbers are represented by a leading 0). 9^3 = 729. However this includes 000, so we subtract 1, leaving 728, B.