Quy tắc tính giá trị biểu thức lớp 3 & cách giải chi tiết

Calculating the value of expressions in grade 3 is one of the basic but important mathematical knowledge and forms that often appears in exams. Therefore, in the following article, Nguyễn Tất Thành will share details about how to calculate expression values, along with some common types of exercises and solution methods for you to understand clearly.

Knowledge to remember when calculating the value of math expressions in grade 3

If in the math program for grades 1 and 2, students only get acquainted with exercises with individual calculations. However, when entering 3rd grade math, students will be introduced to math problems that have many calculations combined together, requiring them to calculate. This is “the validity of expressions”.

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Concept of expressions and expression values

In mathematics, numerical expressions are calculations and numbers combined together. When we solve those calculations, we will get a result called the value of the expression.

Therefore, the value of the expression: Is the result after performing the calculations in the expression.

Types of expressions and order of calculation

The types of math exercises for grade 3 are quite diverse, especially the expressions section will have the following forms and order:

Type 1: Expression contains only calculations of the same priority: Addition, subtraction or multiplication, division: Perform calculations from left to right.

For example: Calculate the expression value:

a) 93 : 3 x 7 b) 15 x 7 : 5

Solution instructions

a) 93 : 3 x 7 = 31 x 7 = 217

b) 15 x 7 : 5 = 105 : 5 = 21

Type 2: Expression includes addition, subtraction, multiplication, and division operations. We perform multiplication and division first, addition and subtraction later;

For example: Write the following expressions and calculate their values:

a) Calculate the product of 15 and 4 and add it to 42.

b) Calculate the sum of 98 and 37 and then subtract 74.

Solution instructions

a) 15 x 4 + 42 = 60 + 42 = 102.

b) 98 + 37 – 74 = 135 – 74 = 61.

Form 3: Expression contains parentheses ( ), we will perform the calculation inside the parentheses first, outside the parentheses later.

For example: Calculate the value of the following expressions:

a) 99927 : (10248:8 – 1272)

b) (10356×5 – 780): 6

Instruct:

a) 99927 : (10248:8 – 1272) = 99927 : (1281 – 1272) = 99927 : 9 = 11103.

b) (10356×5 – 780) : 6 = (51780 – 780) : 6 = 51000 : 6 = 8500

Attention:

Case 1: If the expression has multiplication and division that are not adjacent, but between the calculations there is an addition or subtraction sign, then we will perform both the multiplication and division operations at the same time. Then continue to consider the signs of the remaining calculations in the expression and apply the above-mentioned expression forms.

Example: 128 × 2 + 367 × 3 – 895 + 476 × 4 – 2018 + 182

= 256 + 1101 – 895 + 1904 – 2018 + 182

= 1357 – 895 + 1904 – 2018 + 182

= 462 + 1904 – 2018 + 182

= 2366 – 2018 + 182

= 348 + 182

= 530

Or 128 × 2 + 367 × 3 – 895 + 476 × 4 – 2018 + 182

= 256 + 1101 – 895 + 1904 – 2018 + 182

= 1357 – 895 + 1904 – (2018 – 182)

= 462 + 1904 – 1836

= 2366 – 1836

= 530

Case 2: If the expression has division and multiplication next to each other, we will have to do it in order from left to right instead of calculating multiplication first and then division. After that, we will continue to consider the remaining calculation signs in the expression according to the given rules.

Example: 195615 : 945 × 13 – 356 + 1024

= 207 × 13 – 356 + 1024

= 2691 – 356 +1024

= 2335 + 1024

= 3359

Rules for calculating the value of class 3 expressions

Based on the above expression types, we can derive important rules when calculating the following expression values:

• Expressions have only two operations, addition and subtraction or multiplication and division, so we just need to do them in order from left to right.

• Expressions include addition, subtraction, multiplication and division, so everyone needs to follow the rule “multiply and divide first, add and subtract later”.

• In an expression containing parentheses (), we will have to perform the calculation inside the parentheses first and then outside the parentheses.

Instructions for solving exercises in the 3rd grade math textbook to calculate the value of expressions

Below are some exercises in the 3rd grade math curriculum along with solution instructions for your further reference:

Lesson 1: Calculating the value of expressions: (page 79)

a) 205 + 60 + 30

268 – 68 + 17

b) 462 – 40 + 70

287 – 7 – 80

Solution instructions

a) 205 + 60 + 30 = 265 + 30

= 295

268 – 68 + 17 = 200 + 17

= 217

b) 462 – 40 + 70 = 422 + 70

= 492

287 – 7 – 80 = 280 – 80

= 200

Lesson 2: Calculating the value of expressions (page 79)

a) 15 × 3 × 2

48 : 2 : 6

b) 8 × 5 : 2

81 : 9×7

Solution instructions

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: (page 79) Fill in marks; = in the dot below

55 × 5 : 3 …. 32

47 ….. 84 – 34 – 3

20 + 5 ….. 40 : 2 + 6

Solution instructions

55 × 5 : 3 > 32

47 = 84 -34 – 3

20 + 5

Lesson 4: (page 79) Each package of noodles weighs 80g, each box of milk weighs 455g. How many grams do 2 packs of noodles and 1 box of milk weigh?

Solution instructions

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

80 + 80 + 455 = 615 grams

Answer: 615 grams

Instructions for solving math exercises on page 80 of the textbook:

Lesson 1: (page 80) 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 instructions

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

Exercise 2: (page 80) Write the correct or incorrect information in the space below

a) 37 – 5 × 5 = 12

180 : 6 + 30 = 60

30 + 60 × 2 = 150

282 – 100 : 2 = 91

b) 13 × 3 – 2 = 13

180 + 30 : 6 = 35

10 + 60 × 2 = 180

282 – 100 : 2 = 232

Solution instructions

a) 37 – 5 × 5 = 12 D

180 : 6 + 30 = 60 D

30 + 60 × 2 = 150 VND

282 – 100 : 2 = 91 S

b) 13 × 3 – 2 = 13 S

180 + 30 : 6 = 35 S

10 + 60 × 2 = 180 S

282 – 100 : 2 = 232 D

Lesson 3: (page 80) Mom picked 60 apples, sister picked 35 apples. Mother’s and sister’s apples are all placed in 5 boxes. How many apples are in each box?

Solution instructions

The total number of apples picked by mother and sister is:

60 + 35 = 95 (fruit)

Each box has the following number of apples:

95 : 5 = 19 (fruit)

Exercises for calculating the value of expressions for grade 3 apply

In addition to the expression value calculation exercises in the 3rd grade math textbook, below Nguyễn Tất Thành will synthesize some related exercises so that students can apply knowledge to practice effectively:

Exercise 1: Calculate the value of the following expressions:

150 + 10 x 3 =

40 x 5 – 125 =

90 – 48 : 8 =

135 + 7 x 6 =

69 + 20 : 5 =

132 + 5 x (7 + 8) =

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Exercise 2: Write (T) if correct, write (F) if incorrect in the following blank boxes:

32 – 5 x 5 = 7

180 : 6 + 35 = 75

30 + 60 x 2 = 150

282 – 82 : 2 = 100

30 + 20 x 2 = 80

131 – 32 x 3 = 25

Exercise 3: Two friends, Nam and Huy, went to pick apples in the garden. Nam picked 30 fruits, Huy picked 10 less than Nam. The number of apples the two of you picked were evenly placed into 5 boxes. How many apples does each box contain?

Exercise 4: Fill in signs (>, =,

135 + 5 x 3 …. 125 + 5 x 5

189 : 3 x 8 …. 189 : 9 x 8

12 + 20 x 2 …. 16 + 50 : 2

156 + 20 : 2 …. 156 + 5x 2

145 : 3 + 10 …. 145 – 20 x 2

Exercise 5:

a) (563+ 126 ) x 2

b) 4 x 108 + 157 =

c)1243 – 366 : 3

d)435 : 5 + 582 =

e)153 + 638 – 470 =

Exercise 6: Calculate expression values:

a. 3 x ( 89424 – 72813 )

b. 24368 + 15336 : 3

c. 72009 : 3 x 2

d. 2 x 45000 : 9

e. 15 840 + 32046 : 7

f. 32 464 : 8 – 3956

g. 15 840 + 8972 x 6

i. (12 879 – 9 876) x 4

h. 239 + 1267 x 3=

l. 2505 : ( 403 – 398)=

Exercise 7: Calculate expression values:

(4672 + 3583): 5

1956 + 2126 x 4

4672 – ( 3583 – 193)

2078 – 3328 : 4

Exercise 8: Write the expression and then calculate the value of the expression:

a. 45 divided by 5 multiplied by 7

b. 1535 divided by 5 plus 976

c. 236 multiplied by 2 minus 195

d. 1562 divided by 3 multiplied by 4

Exercise 9: Calculate the value of the following expressions

a) 78 x 6 + 345 c) 56 + 67 x 6

b) 378 + 324 : 3 d) 288 : 6 x 7

Exercise 10. 25x4x7; 216×3 : 6; 990 :3 :6; 480 :8 x 7; 125×2:5

Experience conquering 3rd grade math calculating the value of expressions

For children just entering 3rd grade, solving math problems with many combined calculations will certainly be more difficult than solving math problems like grades 1 and 2. Therefore, to help children conquer this type of math To make it easier to understand and more effective, below are some experiences for you to refer to and apply.

Build a mathematical foundation with Nguyễn Tất Thành Math

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Master the rules for calculating the value of expressions

To calculate the value of an expression, you must clearly understand the 3 rules mentioned above. Parents can explain each rule in detail for children to understand, and regularly check their children’s old knowledge to ensure they avoid the situation of “learning first and forgetting later”.

Do the exercises and practice regularly

Practicing and practicing regularly is considered the best method to help improve knowledge, especially for young children. After grasping the rules and understanding how to solve real expression value calculations, parents should let their children practice regularly, do related exercises every day, or participate in games, solve puzzles, and participate. contests on the internet,…

Through regular training, children’s brains will function better, improve their calculation skills and develop more carefulness when studying effectively.

Experience in teaching expression values ​​through mental math

Mental math is considered a learning method that combines many skills. In addition to solving exercises in books, parents can combine solving math problems with practical, visual teaching aids. Through this, it will help increase your child’s receptive ability and interest in conquering math problems more effectively.

Conclude

Above are the shares about the knowledge of calculating the value of expressions in grade 3 so that children and their parents can refer to it, as well as accompany their children on the journey to conquer this subject and knowledge. If parents plan to learn about tools to help their children learn math more effectively, don’t miss Nguyễn Tất Thành Math.

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