how many numbers between 4000 and 7000 can be choosen using digita 0,1,2,3,4,5,6,7 and 8 if each digit must not be repeated in any numbers?
between means ... 4000 < n < 7000
3 choices for the 1st digit
... 4, 5, 6
8 for the 2nd digit
7 for the 3rd digit
6 for the 4th digit
numbers = 3 * 8 * 7 * 6