What is to be subtracted from 8.1 to get 0.813?

Answer

To solve the problem "What is to be subtracted from 8.1 to get 0.813?", we will follow these steps:

### Step-by-Step Solution:

1. **Understand the Problem**: We need to find a number (let's call it \( x \)) that, when subtracted from 8.1, gives us 0.813. This can be expressed with the equation:
\[ 8.1 - x = 0.813 \]

2. **Rearrange the Equation**: To find \( x \), we can rearrange the equation to isolate \( x \):
\[ x = 8.1 - 0.813 \]

3. **Perform the Subtraction**: Now, we will calculate \( 8.1 - 0.813 \):
- First, align the decimal points:
```
8.100
- 0.813
---------
```
- Now, subtract starting from the right:
- In the thousandths place: \( 0 - 3 \) (we need to borrow, so it becomes \( 10 - 3 = 7 \))
- In the hundredths place: \( 0 - 1 \) (after borrowing, it becomes \( 9 - 1 = 8 \))
- In the tenths place: \( 0 - 8 \) (after borrowing, it becomes \( 10 - 8 = 2 \))
- In the units place: \( 8 - 0 = 8 \)

Putting it all together, we get:
\[ 8.100 - 0.813 = 7.287 \]

4. **Conclusion**: Therefore, the number that needs to be subtracted from 8.1 to get 0.813 is:
\[ x = 7.287 \]

### Final Answer:
The number to be subtracted from 8.1 to get 0.813 is **7.287**.

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