posted by sh .
How many 4-digit whole numbers are there? For example, 1220 is acceptable but 0678 is not.
How do you do permutation and repetition?
since first bar cannot be a zero possibiltiies of first numeral is 9, and since repition is allowed, the last 3 slots are allowed to be 10 therefore,
9 x 10 x 10 x 10 (had u forgotten that it said even or odd numbers only, just simply divide by 2) other than that the answer is 9000.