Get familiar with expressions + Find expression values

### 1.1. Get familiar with the expression

#### 1.1.1. Example of the expression

126 + 51 ; 62 – 11 ; 13 x 3 ; 84 : 4 ; 125 + 10 – 4 ; 125 + 10 – 4 ; 45 : 5 + 7 ; … are expressions.

#### 1.1.2. The value of the expression

126 + 51 = 177. The value of the expression 126 + 51 is 177.

125 + 10 – 4 = 131. The value of the expression 125 + 10 – 4 is 131.

### 1.2. Calculate the value of the expression

*If there are only addition and subtraction operations in the expression, then we perform the calculations in order from left to right.*

60 + 20 – 5 = 80 – 5

= 75

*If in the expression there are only multiplication and division operations, we perform the calculations in order from left to right.*

49 : 7 x 5 = 7 x 5

= 35

*If in the expression there are addition, subtraction, multiplication, and division operations, we perform multiplication and division operations first; Then perform the following addition and subtraction calculations.*

60 + 35 : 5 = 60 + 7

= 67

86 – 10 x 4 = 86 – 40

= 46

- Expressions (30+5) : 5 ; 3 x (20 – 10) … is an expression with brackets ().

*When calculating the value of an expression with brackets (), we first perform the calculations in brackets.*

(30 + 5) : 5 = 35 : 5

= 7

3 x (20 – 10) = 3 x 10

= 30

### 1.3. Textbook exercise solution page 78

**Lesson 1:** Find the value of each of the following expressions (according to the pattern)

The value of the expression 284+10 is 294 |

a) 125+18 ; b) 161–150 ; c) 21×4 ; d) 48:2

**Solution guide:**

- Calculate the value of the operations and fill in the blanks with the results.

a) 125+18 = 143

The value of the expression 125+18 is 143.

b) 161–150 = 11

The value of the expression 161–150 is 11.

c) 21×4 = 84

The value of the expression 21×4 is 84.

d) 48:2 = 24

The value of the expression 48:2 is 24.

**Lesson 2:** What is the value of each of the following expressions?

__Solution guide:__

- Find the values of expressions.
- Match with the appropriate result.

### 1.4. Textbook exercise solution page 79

**Lesson 1:** Calculate the value of the expression

a) 205+60+3

268–68+17

b) 462–40+7

387–7–80

__Solution guide:__

- The expression has only addition and subtraction operations, so we perform the calculations in order from left to right.

a) 205+60+3 = 265+3 = 268

268–68+17 = 200+17 = 217

b) 462–40+7 = 422+7 = 429

387–7–80 = 380−80 = 300.

**Lesson 2:** Calculate the value of the expression

a) 15 × 3 × 2

48 : 2 : 6

b) 8 × 5 : 2

81 : 9 × 7

__Solution guide:__

- Expressions only have multiplication and division, then we perform the calculations in order from left to right.

a) 15 × 3 × 2 = 45 × 2 = 90

48 : 2 : 6 = 24 : 6 = 4

b) 8 × 5 : 2 = 40 : 2 = 20

81:9×7 = 9×7 = 63

**Lesson 3: **Enter the sign >; < or = in the dot

55 : 5 × 3 … 32

47 … 84−34−3

20+5 … 40 : 2+6

__Solution guide:__

- Calculate the value of the sides according to the rules learned.
- Compare and then fill in the blanks with the appropriate mark.

\(\underbrace {55:5 \times 3}_{33} > 32\)

\(47 = \underbrace {84 – 34 – 3}_{47}\)

\(\underbrace {20 + 5}_{25} < \underbrace {40:2 + 6}_{26}\)

**Lesson 4:** Each pack of noodles weighs 80g, each box of milk weighs 455g. How many grams are 2 packs of noodles and 1 box of milk?

__Solution guide:__

* Summary*

1 pack of noodles: 80g

1 box of milk: 455g

2 packs of noodles and 1 box of milk : … g ?

- Find the mass of two packets of noodles.
- Calculate the total weight of two packets of noodles and a carton of milk.

*Solution*

2 packages of noodles weighing in grams are:

80 x 2 = 160 (g)

Both packages of noodles and 1 box of milk weigh in grams:

160+455 = 615 (g)

Answer: 615g.

### 1.5. Textbook exercise solution page 80

**Lesson 1:** Calculate the value of the expression

a) 253+10 × 4 41×5−100 93–48 : 8

b) 500+6 × 7 30 × 8+50 69+20 × 4

__Solution guide:__

- For expressions with addition, subtraction, multiplication, and division, we perform multiplication and division operations first; Then perform the following addition and subtraction calculations.

a) 253+10×4 = 253+40 = 293

41 × 5−100 = 205–100 = 105

93–48 : 8 = 93 – 6 = 87

b) 500+6×7 = 500+42 = 542

30×8+50 = 240+50 = 290

69+20×4 = 69+80 = 149

**Lesson 2:** Correct write D, false write WILL

a) 37−5×5 = 12 b) 13×3−2 = 13

180:6+30 = 60 180+30:6 = 35

30+60×2 = 150 30+60×2 = 180

282−100:2 = 91 282−100:2 = 232

__Solution guide:__

- Evaluate expressions.
- Compare with the given results and then fill in the blanks with the appropriate T or S.

a) 37−5×5 = 37−25 = 12 (Fill in the blank)

180:6+30 = 30+30 = 60 (Fill T in the blank)

30+60×2 = 30+120 = 150 (Fill T in the blank)

282−100:2 = 282−50 = 232 (Insert S in the box)

b) 13×3−2 = 39−2 = 37 (Insert S in the blank)

180+30:6 = 180+5 = 185 (Insert S in the box)

30+60×2 = 30+120 = 150 (Insert S in the box)

282−100:2 = 282−50 = 232 (Fill in the blanks)

Fill in the blanks in order from top to bottom:

a) D, D, D, S.

b) S, S, S, D.

**Lesson 3:** Mother picked 6060 apples, sister picked 3535 apples. The apples of both mother and sister are evenly arranged in 55 boxes. How many apples are there in each box?

__Solution guide:__

*Summary*

Mother: 60 fruits

Sister: 35 fruits

Put in 5 boxes

Each box : … fruit?

- Find the total number of fruits picked by mother and sister.
- Divide the number of fruits you just found by 5.

*Solution*

Mother and sister picked all the apples:

60+35 = 95 (fruit)

The number of apples in each box is:

95:5 = 19 (fruit)

Answer: 19 balls.

**Lesson 4:**

Given 8 triangles, each shape as shown below:

Arrange it in the form below:

__Solution guide:__

- Divide the quadrilateral into the given triangles, thereby finding the appropriate puzzle.

Can be arranged as shown below:

### 1.6. Textbook exercise solution page 82

**Lesson 1:** Calculate the value of the expression

a) 25 – (20-10)

80–(30+25)

b) 125 + (13+7)

416 – (25-11)

__Solution guide:__

- Expressions containing brackets perform the calculations in brackets first.

a) 25 – (20–10) = 25–10 = 15

80 – (30+25) = 80–55 = 25

b) 125 + (13+7) = 125+20 = 145

416 – (25–11) = 416–14 = 402.

**Lesson 2:** Calculate the value of the expression

a) (65+15)×2

48 : (6:3)

b) (74–14) : 2

81 : (3×3)

__Solution guide:__

- Expressions containing brackets perform the calculations in brackets first.

a) (65+15)×2 = 80×2 = 160

48:(6:3) = 48:2 = 24

b) (74–14):2 = 60:2 = 30

81:(3×3) = 81:9 = 9.

**Lesson 3: **There are 240 books arranged evenly into 2 cabinets, each cabinet has 4 drawers. How many books are there in each drawer, given that each shelf has the same number of books?

__Solution guide:__

- Find the number of books in each cabinet: Divide the total number of books by 2.
- Find the number of books in each drawer: Divide the number you just found by 4.

*Solution*

A cabinet with the number of books is:

240:2 = 120 (book)

The number of books in each compartment is:

120:4 = 30 (book)

Answer: 30 books.

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