Write the following in Roman numeral.
400

Answer

To convert the number 400 into Roman numerals, we can follow these steps:

### Step-by-Step Solution:

1. **Understand Roman Numerals**: First, we need to know the basic Roman numeral symbols and their values:
- I = 1
- V = 5
- X = 10
- L = 50
- C = 100
- D = 500
- M = 1000

2. **Identify the Value of 400**: The number we need to convert is 400. We can express this in terms of Roman numeral values.

3. **Break Down the Number**: We can see that 400 can be represented as 500 (D) minus 100 (C). This is because in Roman numerals, we can subtract a smaller numeral from a larger one to indicate a difference.

4. **Write the Roman Numeral**: Therefore, we can write 400 as:
- D (which represents 500) minus C (which represents 100) gives us:
- CD (C before D indicates that we are subtracting 100 from 500).

5. **Final Answer**: Thus, the Roman numeral for 400 is **CD**.