how many 4 digits numbers can be formed from the integer 0-9?

Question

a. if the number must be odd and between 4,200 and 6,800(inclusive) without repetition digits
b. the number must be even and less than 7,200 without repetition digits

Answer 1

a. The first would be 4201. Since repetition is not allowed, that eliminates four digits. The next would be 5367. That eliminates four more. The answer is two.

I suppose you mean that repetition is not allowed in any particular number.

Answer 2

6000