The problem of less than

### 1.1. Knowledge to remember

The solution to the problem has less to do with one quantity than another.

### 1.2. Math form

**General math:** The problem requires finding the value of quantity A, knowing the value of B and A having a value less than B n units.

**Solution method:**

– Read and analyze the topic.

– Determine the quantity with large and small values, the relationship between the quantities. Usually, to find the value of a smaller quantity, we use subtraction.

– Present the solution to the problem.

– Check the results you just found.

### 1.3. Solving Textbook Exercises Page 30

**Lesson 1**

Mai’s garden has 17 orange trees, Hoa’s garden has 7 oranges less than Mai’s garden. How many orange trees are there in Hoa’s garden?

**Summary**

__Solution method__

To find the solution, we subtract 7 orange trees from Mai’s house.

__Solution guide__

The number of orange trees in Hoa’s garden is:

17 – 7 = 10 (orange tree)

Answer: 10 orange trees.

Lesson 2

An is 95cm tall, Binh is 5cm lower than An. How many centimeters tall is Binh?

__Solution method__

**Summary**

An : 95cm

Lower than An: 5cm

Binh: ….cm?

**The answer**

To find the solution, we subtract 5cm from An’s height.

__Solution guide__

The height of the jar is:

95 – 5 = 90 (cm)

Answer: 90 cm.

lesson 3

Class 2A has 15 girls, the number of boys in the class is 3 less than the number of girls. How many boys are there in class 2A?

__Solution method__

**Summary**

Girl: 15 students

Less boys than girls: 3 friends

Boy: … student?

**The answer**

To find the solution, we subtract 3 girls from the number of students.

__Solution guide__

The number of boys in class 2A is:

15 – 3 = 12 (students)

Answer: 12 students.

### 1.4. Textbook exercise solution page 31

**Lesson 1**

– How many stars are there in the circle?

– How many stars are there in the square?

– How many stars are there in a square than in a circle?

– How many stars are there in a circle less than in a square?

b) How many more stars must you draw in the circle so that the number of stars in the two shapes is the same?

__Solution method__

– Count the number of stars in circles and squares.

– Subtract the number of stars in the square from the number of stars in the circle.

– Draw more stars with the result of the subtraction just calculated.

__Solution guide__

a) – In the circle there are 5 stars.

– There are 7 stars in the square.

– There are more stars in the square than in the circle (7 – 5 = 2)

– In the circle there are less than 2 stars in the square (7 – 5 = 2)

b) You have to draw 2 more stars inside the circle so that the number of stars in the two shapes is equal

**Lesson 2**

Solve the problem according to the following summary:

English: 16 years old

I’m 5 years older than you

Me: … age?

__Solution method__

To find your age, subtract 5 years from your age.

__Solution guide__

My age is:

16 – 5 = 11 (age)

Answer: 11 years old.

**lesson 3**

Solve problems according to the following summary:

Me: 11 years old

I’m 5 years older than you

English: … age?

__Solution method__

To find his age, add your age to 5 years.

__Solution guide__

His age is:

11 + 5 = 16 (age)

Answer: 16 years old.

**Lesson 4**

The first building has 16 floors, the second building has 4 floors less than the first building. How many floors does the second building have?

__Solution method__

Building 1: 16 floors

Building 2 is less than building 1: 4 floors

Building 2: … floor?

To find the solution, we subtract 4 from the number of floors of the first building.

__Solution guide__

The second building has the number of floors:

16 – 4 = 12 (floor)

Answer: 12 floors.

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