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The problem provided is asking to calculate the mean (average) of grouped data using the **class-mark method** ("tanda-kelas" in Indonesian).

The table includes:
- **Class intervals** (Kelas interval): These are the ranges of values.
- **Frequency** (f): This represents the number of occurrences for each class interval.

### Step-by-Step Solution

1. **Calculate Class Mark (tanda-kelas):**
   The class mark for each interval is the midpoint, calculated as:

   \[
   \text{Class mark} = \frac{\text{Lower limit} + \text{Upper limit}}{2}
   \]

2. **Multiply Frequency (f) by Class Mark:**
   Multiply the frequency of each interval by the corresponding class mark.

3. **Calculate Mean:**
   The formula for the mean is:

   \[
   \bar{x} = \frac{\sum (f \times x)}{\sum f}
   \]
   where:
   - \( f \) is the frequency.
   - \( x \) is the class mark.
   - \( \sum f \) is the total frequency.

### Calculations:

| No urut | Kelas interval | \( f \) | Class Mark \( x \) | \( f \times x \) |
|--------|----------------|--------|--------------------|------------------|
| 1      | 20 - 24        | 2      | \(\frac{20+24}{2} = 22\) | \( 2 \times 22 = 44 \) |
| 2      | 25 - 29        | 5      | \(\frac{25+29}{2} = 27\) | \( 5 \times 27 = 135 \) |
| 3      | 30 - 34        | 13     | \(\frac{30+34}{2} = 32\) | \( 13 \times 32 = 416 \) |
| 4      | 35 - 39        | 17     | \(\frac{35+39}{2} = 37\) | \( 17 \times 37 = 629 \) |
| 5      | 40 - 44        | 17     | \(\frac{40+44}{2} = 42\) | \( 17 \times 42 = 714 \) |
| 6      | 45 - 49        | 6      | \(\frac{45+49}{2} = 47\) | \( 6 \times 47 = 282 \) |

\[
\sum f = 60, \quad \sum (f \times x) = 2220
\]

### Mean Calculation:

\[
\bar{x} = \frac{2220}{60} = 37
\]

So, the mean of the grouped data is **37**.

Would you like further details or clarification?

Here are 5 related questions you could explore:
1. What is the importance of using class marks in grouped data?
2. How would the mean change if the class intervals were different but the frequencies stayed the same?
3. How can we calculate the mode and median for this grouped data?
4. What is the difference between grouped and ungrouped data in statistics?
5. How does the class width affect the accuracy of the calculated mean?

**Tip**: Always double-check your class marks and frequency products to avoid simple calculation errors when dealing with grouped data.

Hitung nilai rata-rata data berkelompok di bawah ini dengan menggunakan cara 'tanda-kelas'.

Learn how to calculate the mean of grouped data using the class-mark method. This involves determining the midpoints of class intervals and applying the mean formula. Perfect for students in Grades 10-12.

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