Two-digit numbers

### 1.1. Knowledge to remember

– Recognize numbers, know how to read, write, count numbers from 20 to 99

– Recognize the order of the numbers in the 99 . range

– In a two-digit number, the first digit is the tens number, the second number is the unit number.

### 1.2. Math Forms on Two-digit Numbers

**Type 1: Read and write two-digit numbers**

a) Reading two-digit numbers: For numbers with tens other than 1, you read the tens number, pair it with the digit and then read the number of units.

Note: Some special cases are as follows:

- If the unit digit is 1, it is read as ‘fashion’
- If the unit digit is 4, it is read as “four”.
- If the unit digit is 5, it is read as “five”.

b) Write a two-digit number

– Based on the reading of two-digit numbers, you determine the tens and units digits

– Match in order of tens digit and then unit digit to write numbers.

**Form 2: Numerical analysis of two-digit numbers**

In a two-digit number, the first digit is the tens number and the second digit is the unit number.

**Form 3: Order of two-digit numbers**

The range of numbers from 20 to 30 is: 20; 21; 22; 23; 24; 25; 26; 27; 28; 29; 30

– I count consecutive numbers by keeping the tens unchanged (for example, the above sequence has the number of tens as 2, and the digits of the units are counted in ascending order from 0 to 9.

– The next number of a two-digit number where the units row is 9 is a round number with tens being increased by 1 (the next number of 29 is the number 30).

Similarly, you can count two-digit numbers in ascending or descending order.

### 1.3. Solve textbook exercises pages 136, 137

**Lesson 1 page 136**

a) Write the number

Twenty, twenty-one, twenty-two, twenty-three, twenty-four, twenty-five, twenty-six, twenty-seven, twenty-eight, twenty-nine.

b) Write numbers under each line of the number ray and then read the numbers:

**Solution method**

– From the given reading, determine the tens and units numbers and then write the two-digit numbers.

– Count down from 19 and then fill in the missing number in the number line.

__Solution guide__

a) Write the numbers as: 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, respectively.

b)

Read the numbers as

19: Nineteen

20: Twenty

21: Twenty-one

22: Twenty-two

23: Twenty-three

24: Twenty-four

25: Twenty-five

26: Twenty-six

27: Twenty-seven

28: Twenty-eight

29: Twenty-nine

30: Thirty

31: Thirty-one

32: Thirty-two

**Lesson 2 page 137**

Write numbers:

Thirty, thirty-one, thirty-two, thirty-three, thirty-four, thirty-five, thirty-six, thirty-seven, thirty-eight, thirty-nine.

__Solution method__

Identify the tens and units digits and then write the appropriate two-digit number.

Solution guide

Write the numbers as: 30, 31, 32, 33, 34, 35, 36, 37, 38, 39.

**Lesson 3 page 137**

Write numbers:

Forty, forty-one, forty-two, forty-three, forty-four, forty-five, forty-six, forty-seven, forty-eight, forty-nine, fifty.

**Solution method**

Identify the tens and units digits and then write the appropriate two-digit number.

__Solution guide__

Write the numbers as: 40, 41, 42, 42, 44, 45, 46, 47, 48, 49, 50.

**Lesson 4 page 137**

Write the appropriate numbers in the blanks and then read the numbers:

__Solution method__

Count up the numbers and then fill in the missing numbers in the blanks, read the numbers just written.

**Solution guide**

**Figure 1:**

25 reads as twenty-five.

27 reads as twenty-seven

28 reads as twenty-eight.

29 reads as twenty-nine.

31 reads as thirty-one

32 reads as thirty-two

33 reads as thirty-three.

34 reads as thirty-four.

35 reads as thirty-five.

**Figure 2:**

36 reading is thirty-six.

37 reads as thirty-seven.

39 reads as thirty-nine.

40 reading is forty.

41 reading is forty-one.

43 reads as forty-three.

44 reads as forty-four.

45 reading is forty-five.

**Figure 3:**

39 reads as thirty-nine.

41 reading is forty-one.

42 reads as forty-two.

43 reads as forty-three.

44 reads as forty-four.

46 reading is forty-six.

47 reads as forty-seven.

48 reading is forty-eight.

49 reads as forty-nine.

### 1.4. Solve textbook exercises pages 138, 139

**Lesson 1 page 138**

Write numbers:

Fifty, fifty-one, fifty-two, fifty-three, fifty-four, fifty-five, fifty-six, fifty-seven, fifty-eight, fifty-nine.

**Solution method**

Identify the tens and units digits and then write the two-digit number.

__Solution guide__

The numbers are: 50, 51, 52, 53, 54, 55, 56, 57, 58, 59.

**Lesson 2 page 139**

Write numbers:

Sixty, sixty-one, sixty-two, sixty-three, sixty-four, sixty-five, sixty-six, sixty-seven, sixty-eight, sixty-nine, seventy.

__Solution method__

Identify the tens and units digits and then write the two-digit number.

__Solution guide__

The numbers are: 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70.

**Lesson 3 page 139**

Write the correct number in the blank:

__Solution method__

Count down from 30 and then fill in the appropriate number in the blank.

__Solution guide__

**Lesson 4 page 139**

Correct write d, false write s:

__Solution method__

Read the given comments and then check and fill in the blanks with dd or s.

**Solution guide**

### 1.5. Solve textbook exercises pages 140, 141

**Lesson 1 page 140**

Write numbers:

Seventy, seventy-one, seventy-two, seventy-three, seventy-four, seventy-five, seventy-six, seventy-seven, seventy-eight, seventy-nine, eighty.

**Solution method**

Determine the tens and units digit from the given reading and then write the two digit number.

__Solution guide__

The numbers are: 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80.

**Lesson 2 page 141**

Write the appropriate numbers in the blanks and then read the numbers:

__Solution method__

– Count up the numbers and then fill in the missing number in the blank.

– Read the numbers in the sequence above.

__Solution guide__

a) Read the numbers in turn:

81, read as eighty-one.

82, read as eighty-two.

84, read as eighty-four.

85, read as eighty-five.

86, read as eighty-six.

87, read as eighty-seven.

88, read as eighty-eight.

89, read as eighty-nine.

b) Read the numbers in turn:

89, read as eighty-nine.

91, read as ninety-one.

92, read as ninety-two.

93, read as ninety-three.

94, read as ninety-four.

95, read as ninety-five.

96, read as ninety-six.

98, read as ninety-eight.

**Lesson 3 page 141**

Write (in the form):

a) Number 76 includes 7 tens and 6 units.

b) Number 95 includes…tens and …units.

c) Number 83 includes…tens and …units.

d) Number 90 includes…tens and …units.

__Solution method__

Break down two-digit numbers into tens and units.

__Solution guide__

a) Number 76 includes 7 tens and 6 units.

b) Number 95 includes 9 tens and 5 units.

c) Number 83 includes 8 tens and 3 units.

d) The number 90 consists of 9 tens and 0 units.

**Lesson 4 page 141**

How many bowls are there in the picture?

Among them, how many tens and units?

__Solution method__

– Count the number of bowls in each stack and then write the appropriate number.

– Analyze the number by how many tens and how many units.

**Solution guide**

There are 33 bowls in all.

Among them are 3 tens and 3 units.

.

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