Students measure the length of the green bars using the metric ruler segments provided.

To solve the problem of determining the length of each green bar in centimeters using the metric ruler, we need to carefully observe the starting and ending points of each bar on the ruler. Here's a step-by-step explanation:

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Step 1: Understand the Metric Ruler

- The metric ruler is marked in centimeters (cm) and millimeters (mm).
- Each large division represents 1 cm.
- Each small division between the large divisions represents 1 mm (0.1 cm).

Step 2: Measure Each Green Bar

We will measure the length of each green bar by noting its starting point and ending point on the ruler.

#### Bar 1:
- Starting point: 57.0 cm
- Ending point: 61.0 cm
- Length = Ending point - Starting point = 61.0 cm - 57.0 cm = 4.0 cm

#### Bar 2:
- Starting point: 20.0 cm
- Ending point: 23.0 cm
- Length = 23.0 cm - 20.0 cm = 3.0 cm

#### Bar 3:
- Starting point: 61.0 cm
- Ending point: 68.0 cm
- Length = 68.0 cm - 61.0 cm = 7.0 cm

#### Bar 4:
- Starting point: 79.0 cm
- Ending point: 88.0 cm
- Length = 88.0 cm - 79.0 cm = 9.0 cm

#### Bar 5:
- Starting point: 64.0 cm
- Ending point: 72.0 cm
- Length = 72.0 cm - 64.0 cm = 8.0 cm

#### Bar 6:
- Starting point: 53.0 cm
- Ending point: 61.0 cm
- Length = 61.0 cm - 53.0 cm = 8.0 cm

#### Bar 7:
- Starting point: 11.0 cm
- Ending point: 15.0 cm
- Length = 15.0 cm - 11.0 cm = 4.0 cm

#### Bar 8:
- Starting point: 72.0 cm
- Ending point: 80.0 cm
- Length = 80.0 cm - 72.0 cm = 8.0 cm

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Step 3: Record the Results

Now, we write down the lengths of each bar in the provided spaces:

1. 4.0 cm
2. 3.0 cm
3. 7.0 cm
4. 9.0 cm
5. 8.0 cm
6. 8.0 cm
7. 4.0 cm
8. 8.0 cm

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Final Answer:

\[
\boxed{4.0, 3.0, 7.0, 9.0, 8.0, 8.0, 4.0, 8.0}
\]