Math 2 Lesson: Millimeters

### 1.1. Knowledge to remember

– Units of length in millimeters, the symbol and magnitude of millimeters, the relationship of millimeters to centimeters and meters.

– Add and subtract operations with millimeters and related puzzles.

### 1.2. Math forms

**Form 1: Converting units of measurement**

I remember how to convert the units: 1cm = 10mm, 1m = 1000mm.

**Form 2: Perform addition and subtraction with units of length millimeters**

For numbers with the same unit of measure, add or subtract the numbers and keep the unit of measure in the result.

**Form 3: Find the perimeter of a triangle**

To find the perimeter of a triangle, you need to find the sum of the lengths of the sides of the triangle. (Same unit of measure)

### 1.3. Solving Textbook Exercises page 153

**Lesson 1**

Number?

1cm = …mm 1000mm = …m 5cm = …mm

1m = …mm 10mm = …cm 3cm = …mm

__Solution method__

Apply the knowledge you have learned about units of measurement and then fill in the blanks with the appropriate number.

1cm = 10mm; 1m = 1000mm.

__Solution guide__

1cm = 10mm 1000mm = 1m 5cm = 50mm

1m = 1000mm 10mm = 1cm 3cm = 30mm

**Lesson 2**

How many millimeters is each of the following lines?

__Solution method__

Read the lengths of the measured lines.

**Attention: **1cm = 10mm.

__Solution guide__

The straight line MN is 60mm long.

Line segment AB is 30mm long.

The CD straight segment is 70mm long.

**lesson 3**

24mm, 16mm and 28mm.

__Solution method__

The perimeter of a triangle is equal to the sum of the lengths of its sides (in the same units).

__Solution guide__

The perimeter of the triangle is:

24 + 16 + 28 = 68 (mm)

Answer: 68mm.

**Lesson 4**

a) The thickness of the book “Math 2” is about 10…

b) The thickness of the flat ruler is 2…

c) The length of the ballpoint pen is 15…

__Solution method__

Enter the appropriate length unit when measuring the thickness or length of objects.

__Solution guide__

a) The thickness of the book “Math 2” is about 10mm.

b) The thickness of the flat ruler is 2mm.

c) The length of the ballpoint pen is 15cm.

**Attention when solving:** The thickness of common objects is measured in millimeters.

### 1.4. Solving Textbook Exercises page 154

**Lesson 1**

Calculate:

13m + 15m = 5km x 2 =

66km – 24km = 18m : 3 =

23mm + 42mm = 25mm : 5 =

__Solution method__

Perform the calculation with the numbers and then write the length unit in the result you just found.

__Solution guide__

13m + 15m = 28m 5km x 2 = 10km

66km – 24km = 42km 18m : 3 = 6m

23mm + 42mm = 65mm 25mm : 5 = 5mm

**Lesson 2**

A person travels 18km to the town, then another 12km to the city. How many kilometers did he travel in all?

__Solution method__

To calculate how many kilometers that person has traveled, we calculate the sum of the lengths of the two given distances.

__Solution guide__

The distance traveled by the person is:

18 + 12 = 30 (km)

Answer: 30 km.

**lesson 3**

Choose a letter that has a right answer:

A tailor uses 15m of fabric to sew 5 sets of the same clothes. How many meters of fabric are needed to make such a garment?

A. 10m

B. 20m

C. 3m

__Solution method__

To find the solution, we divide the number of meters of fabric by the number of clothes.

__Solution guide__

We have: 15 : 5 = 3 (m)

**Circle the letter C.**

**Lesson 4**

Measure the lengths of the sides of triangle ABC and then calculate the perimeter of that triangle.

__Solution method__

Use a straightedge with centimeter divisions to measure the lengths of the sides of the triangle.

– The perimeter of a triangle is equal to the sum of the lengths of its three sides (calculated in the same units).

__Solution guide__

Measure the lengths of the sides of triangle ABC, we get:

AB = 3cm, AC = 4cm, BC = 5cm.

The perimeter of triangle ABC is:

3 + 4 + 5 = 12 (cm)

Answer: 12cm.

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