The number lock of a suitcase has 4 wheels, each labelled with ten digits i.e.,

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 $={ }^{10} \mathrm{C}_{4}$

$\therefore$ Number of four digits with no repetitions $={ }^{10} \mathrm{C}_{4} \times\left\lfloor 4=\frac{\lfloor 10}{|4| 6} \times\lfloor 4=7 \times 8 \times 9 \times 10=5040\right.$

There is only one number that can open the suitcase.

Thus, the required probability is $\frac{1}{5040}$.