Seconds, centuries

### 1.1. Knowledge to remember

**a) Seconds**

*1 hour = 60 minutes*

*1 minute = 60 seconds*

**b) Century **

*1 century = 100 years*

- From year 1 to 100 is the first century (first century)
- From the year 101 to the year 200 is the second century (second century).
- From 201 to 300 is the third century (III century).

………….

- From 1901 to 2000 was the twentieth century (twentieth century).
- From 2001 to 2100 is the twenty-first century (21st century).

### 1.2. Textbook exercise solution page 25

**Lesson 1: **Write the correct number in the dot

a) 1 minute = … seconds 2 minutes = … seconds

60 seconds = … minutes 7 minutes = … seconds

1313 minutes = … seconds 1 minute 8 seconds = … seconds

b) 1 century = …year 5 century =…year

100 years = …..th century 9th century =…years

1212 century = …year 1515 century = ….year

**Solution guide:**

Based on the conversion methods:

* 1 hour = 60 minutes*

* 1 minute = 60 seconds*

* 1 century = 100 years*

a) 1 minute = 60 seconds 2 minutes = 120 seconds

60 seconds = 1 minute 7 minutes = 420 seconds

\(\frac{1}{3}\) minutes = 20 seconds 1 minute 8 seconds = 68 seconds

b) 1 century = 100 years 5 centuries = 500 years

100 years = 1 century 9 century = 900 years

\(\frac{1}{2}\) century = 50 years \(\frac{1}{5}\) century = 20 years

**Lesson 2:**

a) Uncle Ho was born in 1890. What century was Uncle Ho born in?

Uncle Ho left to find a way to save the country in 1911. What century was that year?

b) The August Revolution was successful in 1945. Which century was that year?

c) Mrs. Trieu led the uprising against the Dong Ngo army in 248. Which century was that year?

__Solution guide:__

- From year 1 to year 100 is the first century (first century).
- From 101 to 200 is the second century (second century).
- From 201 to 300 is the third century (III century).

………….

- From 1901 to 2000 was the twentieth century (twentieth century).
- From 2001 to 2100 is the twenty-first century (21st century).

a) Uncle Ho was born in 1890. Uncle Ho was born in the nineteenth century.

Uncle Ho left to find a way to save the country in 1911. That year belonged to the twentieth century.

b) The August Revolution was successful in 1945. That year belonged to the twentieth century.

c) Mrs. Trieu led the uprising against the Dong Ngo army in 248. That year was in the third century.

**Lesson 3:**

a) Ly Thai To moved the capital to Thang Long in 1010. In which century was that year? How many years has it been so far?

b) Ngo Quyen defeated the Southern Han army on Bach Dang river in 938. Which century was that year? How many years has it been so far?

__Solution guide:__

- From year 1 to year 100 is the first century (first century).
- From 101 to 200 is the second century (second century).
- From 201 to 300 is the third century (III century).

………….

- From 1901 to 2000 was the twentieth century (twentieth century).
- From 2001 to 2100 is the twenty-first century (21st century).

a) Ly Thai To moved the capital to Thang Long in 1010. That year belonged to the 11th century.

The number of years so far is: 2018 – 1010 = 1008 (years)

b) Ngo Quyen defeated the Southern Han army on Bach Dang river in 938. That year belonged to the 10th century.

The number of years so far is: 2018 – 938 = 1080 (years).

### 1.3. Textbook exercise solution page 26

**Lesson 1:**

a) Name the months with: 30 days; 31 days; 28 or 29 days

b) Tell: A leap year is a year in which February has 29 days

In non-leap years, February has only 28 days.

Q: How many days are in a leap year? How many days does a non-leap year have?

__Solution guide:__

- Based on how to view the calendar learned in 3rd grade.

a) Months with 30 days are: April, June, September, and November.

Months with 31 days are: January, March, May, July, August, October, December.

The month with 28 (or 29) days is February

b) Leap year has 366 days, non-leap year has 365 days.

**Lesson 2: **Write the correct number in the dot

3 days = … hours \(\frac{1}{3}\) days = … hours 3 hours 10 minutes = … minutes

4 hours = … minutes \(\frac{1}{4}\) hours = … minutes 2 minutes 5 seconds = … seconds

8 minutes = … seconds \(\frac{1}{2}\) minutes = … seconds 4 minutes 20 seconds = … seconds

__Solution guide:__

Based on the conversion methods:

* 1 hour = 60 minutes*

* 1 minute = 60 seconds*

3 days = 72 hours \(\frac{1}{3}\) days = 8 hours 3 hours 10 minutes = 190 minutes

4 hours = 240 minutes \(\frac{1}{4}\) hours = 15 minutes 2 minutes 5 seconds = 125 seconds

8 minutes = 480 seconds \(\frac{1}{2}\) minutes = 30 seconds 4 minutes 20 seconds = 260 seconds

**Lesson 3:**

a) Quang Trung defeated the Qing army in 1789. Which century was that year?

b) The 600th anniversary of Nguyen Trai’s birth was held in 1980. What year was Nguyen Trai born? Which century was that year?

__Solution guide:__

- From year 1 to year 100 is the first century (I century).
- From 101 to 200 is the second century (second century).
- From 201 to 300 is the third century (III century).

………….

- From 1901 to 2000 was the twentieth century (twentieth century).
- From 2001 to 2100 is the twenty-first century (21st century).

a) Quang Trung defeated the Qing army in 1789. That year was in the 18th century.

b) Nguyen Trai was born in :

1980 – 600 = 1380

The year 1380 belongs to the fourteenth century.

**Lesson 4: **In the 60m race. Nam ran all \(\frac{1}{4}\) minutes, Binh ran all \(\frac{1}{5}\) minutes. Who runs faster and faster by how many seconds?

__Solution guide:__

- Convert the measurements to the same unit of measurement as seconds and then compare the results. Whoever runs out of time runs out faster, he runs faster.

We have :

\(\frac{1}{4}\) minutes = 15 seconds \(\frac{1}{5}\) minutes = 12 seconds

Because 12 seconds < 15 seconds, Binh runs faster and faster than the number of seconds is:

15 – 12 = 3 (seconds)

**Lesson 5:** Choose a letter that has a right answer

a) The clock indicates

A. 9 hours 8 minutes B. 8 hours 40 minutes

C. 8 hours 45 minutes D. 9 hours 40 minutes

b) 5kg 8g = ?

A. 58g B. 508g

C. 5008g D. 580g

__Solution guide:__

- Observe the clock to find the time on the clock.
- Based on how to change: 1kg = 1000g.

a) The clock shows 8:40.

Circle B.

b) We have: 1kg = 1000g so 5kg = 5000g.

Therefore: 5kg 8g = 5kg + 8g = 5000g + 8g = 5008g.

So: 5kg 8g = 5008g.

Circle C.

.

=====

## Leave a Reply