Practice worksheet for determining significant digits in various numerical forms.

The image you uploaded is a worksheet titled "Adding by 9," which involves practicing addition problems where one of the addends is always 9. Below, I will explain how to solve these types of problems and provide a general approach.

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General Approach to Adding by 9

When adding any number to 9, there is a simple trick that can make the calculation faster:
1. Add 10 instead of 9: Adding 10 is usually easier because it simply increases the tens place by 1.
2. Subtract 1 from the result: Since you added 10 instead of 9, you need to subtract 1 from the result to correct for the extra 1.

For example:
- To calculate \( 7 + 9 \):
- Add 10 to 7: \( 7 + 10 = 17 \)
- Subtract 1: \( 17 - 1 = 16 \)
- So, \( 7 + 9 = 16 \).

This method works for any number being added to 9.

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Worksheet Explanation

The worksheet contains a grid with rows and columns. Each cell in the grid represents an addition problem where one addend is 9, and the other addend varies. The goal is to fill in the results of each addition problem.

#### Example Problems from the Worksheet:
1. Row 1, Column 1: \( 0 + 9 \)
- Adding 9 to 0 gives \( 9 \).
- Result: \( 9 \)

2. Row 1, Column 2: \( 1 + 9 \)
- Using the trick: Add 10 to 1: \( 1 + 10 = 11 \), then subtract 1: \( 11 - 1 = 10 \).
- Result: \( 10 \)

3. Row 2, Column 3: \( 2 + 9 \)
- Using the trick: Add 10 to 2: \( 2 + 10 = 12 \), then subtract 1: \( 12 - 1 = 11 \).
- Result: \( 11 \)

4. Row 3, Column 5: \( 4 + 9 \)
- Using the trick: Add 10 to 4: \( 4 + 10 = 14 \), then subtract 1: \( 14 - 1 = 13 \).
- Result: \( 13 \)

5. Row 4, Column 8: \( 7 + 9 \)
- Using the trick: Add 10 to 7: \( 7 + 10 = 17 \), then subtract 1: \( 17 - 1 = 16 \).
- Result: \( 16 \)

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Complete Solution

Using the above method, we can fill in the entire grid. Here are the results for all the problems:

| | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|----|
| 1 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
| 2 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 |
| 3 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 |
| 4 | 12 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 |
| 5 | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 |
| 6 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
| 7 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 |
| 8 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 |
| 9 | 17 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 |
| 10 | 18 | 19 | 20 | 21 | 22 | 23 | 24 | 25 | 26 | 27 |

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Final Answer

The completed worksheet should look like the table above. Each cell contains the sum of the row number (first addend) and 9 (second addend).

Boxed Final Answer:
\[
\boxed{
\begin{array}{c|cccccccccc}
& 1 & 2 & 3 & 4 & 5 & 6 & 7 & 8 & 9 & 10 \\
\hline
1 & 9 & 10 & 11 & 12 & 13 & 14 & 15 & 16 & 17 & 18 \\
2 & 10 & 11 & 12 & 13 & 14 & 15 & 16 & 17 & 18 & 19 \\
3 & 11 & 12 & 13 & 14 & 15 & 16 & 17 & 18 & 19 & 20 \\
4 & 12 & 13 & 14 & 15 & 16 & 17 & 18 & 19 & 20 & 21 \\
5 & 13 & 14 & 15 & 16 & 17 & 18 & 19 & 20 & 21 & 22 \\
6 & 14 & 15 & 16 & 17 & 18 & 19 & 20 & 21 & 22 & 23 \\
7 & 15 & 16 & 17 & 18 & 19 & 20 & 21 & 22 & 23 & 24 \\
8 & 16 & 17 & 18 & 19 & 20 & 21 & 22 & 23 & 24 & 25 \\
9 & 17 & 18 & 19 & 20 & 21 & 22 & 23 & 24 & 25 & 26 \\
10 & 18 & 19 & 20 & 21 & 22 & 23 & 24 & 25 & 26 & 27 \\
\end{array}
}
\]