Table of time units

### 1.1. Knowledge to remember

**a) Time units**

1 century = 100 years 1 year = 12 months 1 year = 365 days 1 leap year = 366 days Every 4 years there is a leap year |
1 week = 7 days 1 day = 24 hours 1 hour = 60 minutes 1 minute = 60 seconds |

January, March, May, July, August, October and December have 31 days.

April, June, September, and November have 30 days.

February has 28 days (in a leap year there are 29 days).

**b) Example of time unit conversion**

– One and a half years = 1.5 years = 12 months x 1.5 = 18 months.

– \(\frac{2}{3}\) hours = 60 minutes x \(\frac{2}{3}\) = 40 minutes.

– 0.5 hours = 60 minutes x 0.5 = 30 minutes.

– 216 minutes = 3 hours 36 minutes = 3.6 hours:

216 minutes = 3 hours 36 minutes

216 minutes = 3.6 hours

### 1.2. Solving textbook exercises pages 130, 131

**Lesson 1 Textbook page 130**

In the history of human development, there have been great inventions. The table below shows the names and publication years of some inventions. Read the table and tell which century each invention was published.

__Solution guide:__

- The telescope was invented in the 17th century (XVII).
- Pencil was invented in the 18th century (XVIII).
- The locomotive was invented in the 19th century (XIX).
- Bicycles were invented in the 19th century (XIX).
- Cars were invented in the 19th century (XIX).
- Airplanes invented in the 20th century (XX).
- Electronic computers were invented in the 20th century (XX).
- Artificial satellites were invented in the 20th century (XX).

Lesson 2 Textbook page 131

Write the correct number in the dot:

a) 6 years = …months b) 3 hours = …minutes

4 years 2 months = …months 1.5 hours = …minutes

3 and a half years = ….months \(\frac{3}{4}\) hours = …minutes

3 days = ….hours 6 minutes = … seconds

0.5 days = …hours \(\frac{1}{2}\) minutes = …seconds

3 and a half days = …hours 1 hour = …seconds

__Solution guide:__

a) 6 years = 72 months b) 3 hours = 180 minutes

4 years 2 months = 50 months 1.5 hours = 90 minutes

3 and a half years = 42 months \(\frac{3}{4}\) hours = 45 minutes

3 days = 72 hours 6 minutes = 360 seconds

0.5 days = 12 hours \(\frac{1}{2}\) minutes = 30 seconds

3 and a half days = 84 hours 1 hour = 3600 seconds

Lesson 3 Textbook page 131

Fill in the correct decimal places:

a) 72 minutes = … hours b) 30 seconds = … minutes

270 minutes = … hours 135 seconds = … minutes

__Solution guide:__

a) 72 minutes = \(\frac{72}{60}\) hours = 1.2 hours b) 30 seconds = \(\frac{30}{60}\) minutes = 0.5 minutes

270 minutes = \(\frac{270}{60}\) hours = 4.5 hours 135 seconds = \(\frac{135}{60}\)0 minutes = 2.25 minutes

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