Since it is not mentioned in the problem, we will assume that repeating of number is allowed.
For the first wheel, you have 10 possible digits.
For the second wheel, you have 10 possible digits.
For the third wheel, you have 10 possible digits.
10 x 10 x 10 = 1000
The probability that someone randomly guesses the correct combination in his first attempt is 1/1000.
If this was without repeat, then
10*9*8 = 720
The probability that someone randomly guesses the correct combination in his first attempt is 1/720.
Answer: 
Step-by-step explanation:
Given the following expression:

You can follow these steps in order to solve the exercise:
1. You need to solve the operations inside the parentheses:
- Add the fractions. Since they have different denominators, you have to find the Least Comon Denominator (LCD):

- Solve the division divididing the numerator 0.25 by the denominator 2.
Then, you get:

2. Solve the exponent:

3. Solve the multiplication:

4. Solve the subtraction:

5. Since :

You can write the result as a mixed fraction:
