Total Number of digits = 4
We have to fill two places using the 4 digits without repeating the digits.
The first place digit can be filled in 4 ways. When first place is filled, one number is already taken, so now we can fill the second place using remaining 3 digits (3 ways)
So, the total number of ways of forming 2 digit numbers = 4 x 3 = 12 ways
