1. **State the problem:** We have a lock with 4 wheels, each labeled 0 to 9, and the combination is a sequence of 4 digits with no repeats. We want the probability of guessing the correct combination. 2. **Total number of possible combinations:** Since each wheel has 10 digits and digits cannot repeat, the number of possible combinations is the number of permutations of 10 digits taken 4 at a time. 3. **Formula for permutations:** $$P(n, r) = \frac{n!}{(n-r)!}$$ where $n=10$ and $r=4$. 4. **Calculate permutations:** $$P(10,4) = \frac{10!}{(10-4)!} = \frac{10!}{6!} = 10 \times 9 \times 8 \times 7 = 5040$$ 5. **Probability of guessing right:** There is only 1 correct combination out of 5040 possible. 6. **Probability formula:** $$\text{Probability} = \frac{\text{Number of favorable outcomes}}{\text{Total number of outcomes}} = \frac{1}{5040}$$ **Final answer:** The probability of guessing the right combination is $\frac{1}{5040}$.