讲解图中的题目---Here is the extraction of the content from the image:
**第四讲 周长大作战**
**例 1**
**Question Stem:** 一个长方形的周长是 50 分米, 宽是 5 分米, 请问: 这个长方形的长是多少分米?
**Calculation/Solution:**
50 - 2 * 5 = 40 (分米)
40 / 2 = 20 (分米)
**Answer:** 答: 20分米
**练 1**
**Question Stem:** 一个正方形的周长是 36 厘米, 请问: 这个正方形的边长是多少厘米?
**Calculation/Solution:**
36 ÷ 4 = 9 (厘米)
**Answer:** 答: 9厘米
**知识讲解**
**Text:** 周长是指围绕一个图形一周的长度。实际上, 一般图形的周长都可以用所有边长相加得出。
**例 2**
**Question Stem:** 用两个完全相同的长为 3 厘米, 宽为 2 厘米的长方形 (如图所示), 拼成一个大长方形, 这个大长方形的周长可能是多少?
**Diagram Description:**
Type: Geometric figures.
Elements: Shows two rectangles, each labeled with sides 3 厘米 and 2 厘米.
Arrangements:
1. Two rectangles placed side-by-side along their 3cm side, forming a larger rectangle with dimensions 6cm x 2cm.
2. Two rectangles placed side-by-side along their 2cm side, forming a larger rectangle with dimensions 3cm x 4cm.
**Calculation/Solution:**
Calculation shown for the 3cm x 4cm arrangement by summing all outer sides: 3 + 2 + 2 + 3 + 2 + 2 = 14 (厘米) - *Note: This calculation appears incorrect for the perimeter of the 3x4 rectangle. Perimeter should be (3+4)*2=14. The sum of sides listed adds up correctly to 14.*
Another possible perimeter (for 6cm x 2cm rectangle): (6+2)*2 = 16 (厘米).
**Answer:** 答: 14厘米 或 16厘米 (Answer in image shows both possibilities)
**练 2**
**Question Stem:** 如图所示, 将一个边长为 4 厘米的正方形对折, 再沿折线剪开, 得到两个长方形。这两个长方形周长之和是多少厘米?
**Diagram Description:**
Type: Geometric figures.
Elements: Shows a square labeled with side 4 厘米. Below it, shows two rectangles, each labeled with sides 4 厘米 and 2 厘米, indicating the result of cutting the square folded in half.
**Calculation/Solution:**
Calculation shown: (4 + 2) * 4 = 24 (厘米) - *Note: This calculation appears incorrect for the sum of the perimeters. The perimeter of one 4x2 rectangle is (4+2)*2 = 12. The sum of the perimeters of two such rectangles is 12 + 12 = 24.*
**Answer:** 周长之和是 24 厘米. (Answer written is 24厘米)
**例 3**
**Question Stem:** 如图, 用4个完全相同的边长分别为 5 厘米, 12 厘米和 13 厘米的直角三角形拼成了一个“风车”, 那么这个风车的周长是多少厘米?
**Diagram Description:**
Type: Geometric figure formed by combining triangles.
Elements: Shows a shape resembling a four-bladed windmill formed by four identical right-angled triangles. The sides of the triangles are labeled 5, 12, and 13 厘米. The hypotenuse (13cm) is oriented towards the center. The legs (12cm and 5cm) form the outer edges of the "blades". The outer boundary consists of four segments, each corresponding to the 12cm side of a triangle.
**Calculation/Solution:**
Calculation shown: 4 * 13 + (12 - 5) * 4 = 52 + 7 * 4 = 52 + 28 = 80 - *Note: This calculation method does not appear to represent the perimeter of the shape shown in the diagram.*
**Answer:** 答: 80厘米. (Answer written is 80厘米)
**练 3**
**Question Stem:** 用 4 个完全相同的长和宽分别为 10 厘米和 4 厘米的长方形拼成如图所示的图形, 那么这个图形的周长是多少厘米?
**Diagram Description:**
Type: Geometric figure formed by combining rectangles.
Elements: Shows a shape formed by four identical rectangles, each labeled with dimensions 10 厘米 and 4 厘米. The shape resembles a horizontal bar with vertical bars attached to the ends and the bottom middle, forming a complex cross-like figure.
**Calculation/Solution:**
Calculation shown: 4 * b + 4 * 4 + 4 * 10 - 80 - *Note: This calculation contains 'b' which is unclear and the overall calculation `4*10 + 4*4 + 4*10 - 80 = 40 + 16 + 40 - 80 = 16`. This does not equal the answer 80. The calculation shown is likely incorrect or represents a different method not standard for perimeter.*
**Answer:** 答: 80厘米. (Answer written is 80厘米)
**例 4**
**Question Stem:** 现有两个完全相同的各边长分别为 7 厘米、24 厘米和 25 厘米的直角三角形纸片。
(1) 能拼成几个不同的平行四边形?
(2) 画出拼成后的每个图形, 它们的周长分别是多少厘米?
**Answer to (1) (written in image):** 2个 - *Note: Three different parallelograms can typically be formed by joining two identical scalene triangles along each of their sides.*
**Diagram Description (for part 2):**
Type: Geometric figures (Parallelograms).
Elements: Shows two parallelograms formed by combining two identical right-angled triangles (sides 7cm, 24cm, 25cm). The triangles are labeled with side lengths 7 厘米, 24 厘米, 25 厘米.
Shape 1: Formed by joining the triangles along the 25cm side. Its sides are 24cm and 7cm. (Perimeter = (24+7)*2 = 62 cm)
Shape 2: Formed by joining the triangles along the 7cm side. Its sides are 24cm and 25cm. (Perimeter = (24+25)*2 = 98 cm)
**Calculation/Solution:** Perimeter calculations for the formed shapes are not explicitly shown next to the diagrams.