Question

how many numbers are between 300 and 800 can be made by using digits 2,4,5,6,0?

Answer 1

The first digit can't be 0 or 2, so you have 3 digits for the first choice
The second digit can only be any of the remaining digits, so you have again, 4 choices
The third digit can be any of the remaining digits, that means you have 3 choices

Total numbers you can form = # of first choice * # of second choice * # of third choice
PS: # = number of