8 plus a number: 8+5

### 1.1. Knowledge to remember

– Table plus 8 with a number.

– Apply to solving puzzles with an addition.

– In an addition operation, if the positions of two numbers are changed, the result of that calculation does not change.

### 1.2. Math forms

**Form 1: Performing the calculation**

– Set in vertical columns, numbers in the same row are placed straight together.

– Perform the addition of the numbers of each row in order from right to left.

**Form 2: Mental calculation**

– Calculate the sum of numbers with a value of 10

– Calculate with the remaining numbers.

**Form 3: Math Quiz**

– Read and analyze the problem: Determine the given data, the amount of increase or decrease and the requirements of the problem.

– Find a solution: When the problem requires finding the value of “both” or “all”, I often use addition.

– Presentation of the solution: Write the solution, calculation and answer to the problem.

– Check the solution of the problem and the results just found.

### 1.3. Solving Textbook Exercises

**Lesson 1**

Mental arithmetic:

8 + 3 = 8 + 4 = 8 + 6 = 8 + 7 = 8 + 9 =

3 + 8 = 4 + 8 = 6 + 8 = 7 + 8 = 9 + 8 =

__Solution method__

Add the numbers and fill in the blanks with the result.

__Solution guide__

8 + 3 = 11 8 + 4 = 12 8 + 6 = 14 8 + 7 = 15 8 + 9 = 17

3 + 8 = 11 4 + 8 = 12 6 + 8 = 14 7 + 8 = 15 9 + 8 = 17

Lesson 2

Calculate:

__Solution method__

Add the numbers and fill in the blanks with the result.

__Solution guide__

lesson 3

Mental arithmetic:

8 + 5 = 8 + 6 = 8 + 9 =

8 + 2 + 3 = 8 + 2 + 4 = 8 + 2 + 7 =

9 + 5 = 9 + 8 = 9 + 6 =

9 + 1 + 4 = 9 + 1 + 7 = 9 + 1 + 5 =

__Solution method__

Add the numbers in order from right to left and fill in the blank with the result.

__Solution guide__

8 + 5 = 13 8 + 6 = 14 8 + 9 = 17

8 + 2 + 3 = 13 8 + 2 + 4 = 14 8 + 2 + 7 = 17

9 + 5 = 14 9 + 8 = 17 9 + 6 = 15

9 + 1 + 4 = 14 9 + 1 + 7 = 17 9 + 1 + 5 = 15

Lesson 4

Ha has 8 stamps, Mai has 7 stamps. How many stamps do you both have?

__Solution method__

*Summary*

Ha : 8 stamps

Mai : 7 stamps

Both : … stamps?

**The answer**

To find the solution, we take Ha’s stamps plus Mai’s stamps.

__Solution guide__

Both of you have a stamp number of:

8 + 7 = 15 (stamp)

Answer: 15 stamps.

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