Subtraction (don’t remember) within 1000

### 1.1. Knowledge to remember

How to set the calculation and vertical calculation of subtraction (don’t remember) three-digit numbers.

### 1.2. Math forms

**Form 1: Set and calculate**

– Set the calculation with the corresponding rows to line the columns together: Hundreds of one number line hundreds of another, and so on with tens and units.

– Perform subtraction from right to left.

**Form 2: Mental calculation of subtraction with round numbers**

Perform mental subtraction of hundred round numbers by subtracting the hundreds digits and keeping the tens and units.

**Form 3: Math Quiz**

– Read and analyze problems: Problems for the value of quantities or problems about “more”, “less than”

– Find a solution: To compare the values of numbers, we often use subtraction to find the solution.

– Presenting the solution

– Check the results and the solution of the problem.

### 1.3. Solving Textbook Exercises page 158

**Lesson 1**

Calculate:

__Solution method__

Subtract numbers in the same row from right to left.

__Solution guide__

**Lesson 2**

Calculate then calculate:

548 – 312 ; 732 – 201 ; 592 – 222 ; 395 – 23

__Solution method__

– Set calculation: Write the numbers in the same row and column together.

– Calculation: Subtract numbers in order from right to left.

__Solution guide__

**lesson 3**

Mental calculation (according to the form):

a) 500 – 200 = 300 700 – 300 = 900 – 300 =

600 – 100 = 600 – 400 = 800 – 500 =

b) 1000 – 200 = 800 1000 – 400 = 1000 – 500 =

__Solution method__

Mentally subtract with the numbers thousands and hundreds and then add 2 digits to the end of the result you just found.

__Solution guide__

a) 500 – 200 = 300 700 – 300 = 400 900 – 300 = 600

600 – 100 = 500 600 – 400 = 200 800 – 500 = 300

b) 1000 – 200 = 800 1000 – 400 = 600 1000 – 500 = 500

**Lesson 4**

There are 183 ducks, 121 fewer chickens than ducks. How many chickens are there?

__Solution method__

**Summary**

*The answer*

To find the number of chickens, subtract 121 from the number of ducks.

__Solution guide__

The number of chickens is:

183 – 121 = 62 (child)

Answer: 62 children.

### 1.4. Textbook Exercises Page 159

**Lesson 1**

Calculate:

__Solution method__

Perform subtraction of numbers from right to left.

__Solution guide__

**Lesson 2**

Calculate then calculate:

a) 986 – 264; 758 – 354 ; 831 – 120

b) 73 – 26 ; 65 – 19 ; 81 – 37.

__Solution method__

– Set calculation: Write the digits in the same row and column together.

– Calculation: Subtract numbers in order from right to left.

__Solution guide__

**lesson 3**

Write the correct number in the blank:

__Solution method__

– Find the difference: Subtract the minus number from the subtracted number.

– Find the number to be subtracted: Take the difference of addition and subtraction.

__Solution guide__

First column: 257 – 136 = 121, fill in 121 in the blank.

Second column: 121 + 136 = 257, fill in 257 in the blank.

Third column: 869 – 659 = 210, fill in 210 in the blank.

Fourth column: 867 – 206 = 661, fill in 661 in the blank.

Fifth column: 486 – 264 = 222, fill in 222 in the blank.

**Lesson 4**

Thanh Cong Primary School has 865 students, Huu Nghi Primary School has 32 students less than Thanh Cong Primary School. How many students does Huu Nghi Primary School have?

__Solution method__

**Summary**

*The answer*

To find the solution, we subtract 32 students from Thanh Cong Primary School.

__Solution guide__

The number of students of Huu Nghi Primary School is:

865 – 32 = 833 (student)

Answer: 833 students.

**Lesson 5**

Circle the letter in front of the correct answer:

The number of quadrilaterals in the figure is:

A. 1

B. 2

C. 3

D. 4

__Solution method__

– Counting single quadrilaterals.

– Match the puzzle and then count until all other quadrilaterals.

__Solution guide__

The quadrilaterals are: Figure 2; figure 1+2; figure 2+ 3; figure 1 + 2 + 3.

The given figure has 4 quadrilaterals.

**Circle the letter D.**

### 1.5. Solving Textbook Exercises page 160

**Lesson 1**

Calculate:

__Solution method__

Add in turn from right to left, paying attention to the number to remember.

__Solution guide__

**Lesson 2**

Calculate:

__Solution method__

Subtract the numbers from right to left in turn (note subtraction with memory).

__Solution guide__

**lesson 3**

Mental arithmetic:

700 + 300 = 800 + 200 = 500 + 500 =

1000 – 300 = 1000 – 200 = 1000 – 500 =

__Solution method__

Add or subtract the numbers thousands and hundreds and then add 2 digits to the end of the result.

__Solution guide__

700 + 300 = 1000 800 + 200 = 1000 500 + 500 = 1000

1000 – 300 = 700 1000 – 200 = 800 1000 – 500 = 500

**Lesson 4**

Calculate then calculate:

a) 351 + 216; 427 + 142; 516 + 173

b) 876 – 231; 999 – 542; 505 – 304

__Solution method__

– Set calculation: Write the calculation in a vertical line so that the digits in the same row and column are together.

– Calculation: Add or subtract from right to left respectively.

__Solution guide__

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