How many numbers of four digits can be formed with the digits 1, 2, 3, 4 and 5? (Repetition of digits is not allowed.)

Answer

To determine how many four-digit numbers can be formed using the digits 1, 2, 3, 4, and 5 without repetition, we can follow these steps:

### Step 1: Choose the first digit
We have 5 options for the first digit since we can use any of the digits 1, 2, 3, 4, or 5.

**Choices for the first digit: 5**

### Step 2: Choose the second digit
Once the first digit has been chosen, we cannot use it again (since repetition is not allowed). Therefore, we have 4 remaining options for the second digit.

**Choices for the second digit: 4**

### Step 3: Choose the third digit
After selecting the first and second digits, we are left with 3 digits to choose from for the third digit.

**Choices for the third digit: 3**

### Step 4: Choose the fourth digit
Finally, after choosing the first three digits, we will have 2 digits left to choose from for the fourth digit.

**Choices for the fourth digit: 2**

### Step 5: Calculate the total number of combinations
To find the total number of unique four-digit numbers that can be formed, we multiply the number of choices for each digit together:

\[ \text{Total combinations} = 5 \times 4 \times 3 \times 2 \]

Calculating this gives:

\[ 5 \times 4 = 20 \]
\[ 20 \times 3 = 60 \]
\[ 60 \times 2 = 120 \]

Thus, the total number of four-digit numbers that can be formed is **120**.

### Final Answer:
**120**

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