The number lock has 4 wheels, each labelled with ten digits i.e., from 0 to 9.
Number of ways of selecting 4 different digits out of the 10 digits =10C4
Now, each combination of 4 different digits can be arranged in 4! Ways.
∴ Number of four digits with no repetitions = 4! 10C4 = 5040
There is only one number that can open the suitcase.
Thus, the required probability is 1/5040