Get familiar with statistics

### 1.1. Knowledge to remember

__ Example 1:__ Measuring the height of four friends, Anh, Phong, Ngan, and Minh, we have the following data:

Writing the height measurements of four friends, we get the following data series:

122cm ; 130cm ; 127cm ; 118cm.

Looking at the data series above, we know:

The first number is 122cm, the second number is 130cm, the third number is 127cm, the fourth number is 118cm.

The sequence above has 4 numbers.

__ Example 2:__ Here is the list of children of three families:

Family | Miss Mai | Miss Lan | Miss Hong |

Number of children | 2 | first | 2 |

This table has 2 rows:

– The row above shows the names of the families.

– The bottom row shows the number of children in each family.

Looking at the table above we know:

– The three families listed in the table are: Ms. Mai’s family, Ms. Lan’s family, and Ms. Hong’s family.

– Ms. Mai’s family has 2 children, Ms. Lan’s family has 1 child, and Ms. Hong’s family has 2 children.

### 1.2. Textbook exercise solution page 135

**Lesson 1:** The four friends Dung, Ha, Hung and Quan are in the order of height

129cm; 132cm; 125cm; 135cm.

Based on the data above, answer the following questions:

a) How many centimeters tall is Hung?

How tall is Dung?

How many centimeters tall is Ha?

How many centimeters tall is the army?

b) How many centimeters taller than Hung is Dung?

Ha is how many centimeters shorter than Quan?

Hung and Ha, who is taller? Dung and Quan, who is shorter?

__Solution guide:__

- Based on the given data series, answer your height in turn.
- If you want to compare two people’s height, I subtract the height of the shorter friend from the height of the taller person

a) Hung is 125cm tall.

Dung is 129cm tall.

Ha is 132 cm tall.

Troop is 135cm tall.

b) Dung is 4cm taller than Hung. Because 129 – 125 = 4 (cm).

Ha is 3cm shorter than Quan. Because 135 – 132 = 3 (cm).

Because 132cm > 125cm, Ha is taller than Hung;

Because 129cm < 135cm, Dung is shorter than Quan.

**Lesson 2:** The series of Sundays of February 2004 are the days: 1, 8, 15, 22, 29

Looking at the sequence above, answer the following questions:

a) How many Sundays are there in February 2004?

b) What day is the first Sunday?

c) What is the 22nd Sunday of the month?

__Solution guide:__

- Count the number of numbers in the given data series.
- The order of Sundays is counted from the beginning to the end of the data series.

a) February 2004 has 5 Sundays.

b) The first Sunday is February 1st.

c) The 22nd is the fourth Sunday of the month.

**Lesson 3:** The kilograms of rice in each bag are listed below

Write the series of kilograms of rice for the five bags of rice above:

a) In order from smallest to largest;

b) In order from largest to smallest.

__Solution guide:__

- Compare the given numbers and arrange them in the appropriate order.

We have: 35 kg < 40 kg < 45 kg < 50 kg < 60 kg.

a) Order from smallest to largest: 35kg, 40kg, 45kg, 50kg, 60kg.

b) Order from big to small: 60kg, 50kg, 45kg, 40kg, 35kg.

**Lesson 4:** Given the following data series

5, 10, 15, 20, 25, 30, 35, 40, 45.

Looking at the numbers above, answer the following questions:

a) How many numbers are there in the sequence above? What is the number 25 in the sequence?

b) What is the third number in the sequence? By how many units is this number greater than the first number in the sequence?

c) How much greater is the second number in the sequence?

__Solution guide:__

- Count the number of numbers in the sequence; The order of numbers is counted from left to right.
- Comparing one number by how many more than the other, we subtract the small number from the larger number.

a) The sequence above has all 9 numbers. The number 25 is the fifth number in the sequence.

b) The third number in the sequence is number 15.

This number is greater than the first number, the number of units is:

15 – 5 = 10

c) The second number of the data series is 10.

The first number of the data series is 5.

Since 10 > 5, the second number is larger than the first.

### 1.3. Textbook exercise solution page 136

**Lesson 1: **This is the statistics of the number of excellent students of the 3rd grade in the same elementary school

Class | 3A | 3B | 3C | 3D |

Number of excellent students | 18 | 13 | 25 | 15 |

Based on the table above, answer the following questions:

a) How many good students are there in class 3B? How many good students are there in 3D class?

b) How many good students does class 3C have more than class 3A?

c) Which class has the best students? Which class has the fewest students?

__Solution guide:__

- Read the data in the statistics table and then answer the questions.
- Find the number of good students in class 3C and 3A and subtract the small number from the large number.
- Compare the numbers in the table and then answer the questions.

a) Class 3B has 13 excellent students. Class 3D has 15 excellent students.

b) Class 3C has 7 more good students than class 3A.

c) Class 3C has the most top students (25 students)

Class 3B has the few best students (13 students)

**Lesson 2: **This is the statistics of the number of plants planted in the 3 . block classes

Class | 3A | 3B | 3C | 3D |

The number of trees | 40 | 25 | 45 | 28 |

Look at the table above and answer the following questions:

a) Which class can grow the most trees? Which class can plant the fewest trees?

b) How many trees can two classes 3A and 3C plant in all?

c) How many trees can class 3D plant less than class 3A and more trees than class 3B?

__Solution guide:__

- Read the data in the statistics table and compare.
- Find the number of trees of class 3A and class 3C and then sum the values of the two numbers found.
- Compare how many more or less one number is than the other, then subtract the small number from the larger number.

a) Class 3C planted the most trees. Class 3B planted the fewest trees.

b) Two classes 3A and 3C can plant all 85 trees (40 + 45 = 85 )

c) The 3D class can grow 12 plants less than the 3A class (40 – 28 = 12)

3D layer is 3 trees more than layer 3B (28 – 25 = 3)

**Lesson 3:** Below is a table showing the number of meters of fabric sold by a store in the first three months of the year

Fabric/Month | first | 2 | 3 |

White | 1240m | 1040m | 1475m |

flower | 1875m | 1140m | 1575m |

Looking at the table above, answer the following questions:

a) How many meters of fabric of each type did the store sell in February?

b) In March, how many meters more did the floral fabric sell than the white one?

c) How many meters of floral fabric did the shop sell each month?

__Solution guide:__

- Read the data in the statistics table and then answer the questions of the problem.
- Find the number of meters of flower and white fabric sold in March and subtract the small number from the large number.

a) In February, the store sold 1040m of white fabric and 1140m of floral fabric

b) In March, floral fabric sold 100m more than white fabric.

(1575m – 1475m = 100m)

c) In January, the shop sold 1875 meters of floral fabric.

In February, the store sold 1140 meters of flower fabric

In March, the store sold 1575 meters of floral fabric.

.

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