Divide the measure of time by a number

### 1.1. Knowledge to remember

**a) Example 1:**

Hai played 3 chess games in 42 minutes and 30 seconds. How long on average does Hai play each game of chess?

We have to do the division:

42 minutes 30 seconds : 3 = ?

We calculate and calculate as follows:

So: 42 minutes 30 seconds : 3 = 14 minutes 10 seconds.

**b) Example 2: **

An artificial satellite orbits the Earth 4 times in 7 hours 40 minutes. How long does it take for the satellite to orbit the Earth once?

We have to do the division:

7 hours 40 minutes : 4 = ?

We calculate and calculate as follows:

So: 7 hours 40 minutes : 4 = 1 hour 55 minutes.

### 1.2. Solve textbook exercises on page 136

**Lesson 1 Textbook page 136**

Calculate

a) 24 minutes 12 seconds : 4 ; b) 35 hours 40 minutes: 5;

c) 10 hours 48 minutes : 9 ; d) 18.6 minutes : 6.

*Solution guide:*

Lesson 2 Textbook page 136

A worker works from 7:30 am to 12 pm and can make 3 tools. On average, how long does it take him to make one tool?

*Solution guide:*

That person makes 3 tools out of time:

12 hours – 7 hours 30 minutes = 4 hours 30 minutes

On average, the amount of time it takes for a person to make 1 tool is:

4 hours 30 minutes : 3 = 1 hour 30 minutes

Answer: 1 hour 30 minutes

### 1.3. Solving exercises in the textbook Practice page 137

**Lesson 1 Textbook page 137**

Calculate

a) 3 hours 14 minutes x 3; b) 36 minutes 12 seconds : 3;

c) 7 minutes 26 seconds x 2; d) 14 hours 28 minutes : 7 .

__Solution guide:__

Lesson 2 Textbook page 137

Calculate:

a) (3 hours 40 minutes + 2 hours 25 minutes) × 3;

b) 3 hours 40 minutes + 2 hours 25 minutes × 3;

c) (5 minutes 35 seconds + 6 minutes 21 seconds): 4 ;

d) 12 minutes 3 seconds × 2 + 4 minutes 12 seconds : 4.

__Solution guide:__

a) (3 hours 40 minutes + 2 hours 25 minutes) × 3

= 5 hours 65 minutes × 3 (65 minutes = 1 hour 5 minutes)

= 6 hours 5 minutes × 3

= 18 hours 15 minutes.

b) 3 hours 40 minutes + 2 hours 25 minutes × 3

= 3 hours 40 minutes + 6 hours 75 minutes (75 minutes = 1 hour 15 minutes)

= 3 hours 40 minutes + 7 hours 15 minutes

= 10 hours 55 minutes.

c) (5 minutes 35 seconds + 6 minutes 21 seconds): 4

= 11 minutes 56 seconds : 4

= 2 minutes 59 seconds.

d) 12 minutes 3 seconds × 2 + 4 minutes 12 seconds : 4

= 24 minutes 6 seconds + 1 minute 3 seconds

= 25 minutes 9 seconds.

Lesson 3 Textbook page 137

On average, a worker completes a product in 1 hour and 8 minutes. The first time that person made 7 products. The second time that person makes 8 products. How much time does the person have to work both times?

__Solution guide:__

The first time he makes 7 products out of time is:

1 hour 8 minutes × 7 = 7 hours 56 minutes

The second time that person makes 8 products, the amount of time it takes is:

1 hour 8 minutes × 8 = 9 hours 4 minutes

Both times the person completes the time is:

7 hours 56 minutes + 9 hours 4 minutes = 16 hours 60 minutes

16 hours 60 minutes = 17 hours

Answer: 17 o’clock.

Lesson 4 Textbook page 137

Put >, <, = in the dot:

4.5 hours …. 4 hours 5 minutes

8 hours 16 minutes − 1 hour 25 minutes … 2 hours 17 minutes × × 3

26 hours 25 minutes :: 5 … 2 hours 40 minutes + 2 hours 45 minutes.

__Solution guide:__

- 4.5 hours = 4 hours 30 minutes 30

But 4 hours 30 minutes > 4 hours 5 minutes.

So: 4.5 hours > 4 hours 5 minutes.

- 8 hours 16 minutes − 1 hour 25 minutes

= 7 hours 76 minutes−− 1 hour 25 minutes = 6 hours 51 minutes

2 hours 17 minutes × 3 = 6 hours 51 minutes

So: 8 hours 16 minutes – 1 hour 25 minutes = 2 hours 17 minutes × 3

- 26 hours 25 minutes : 5 = 5 hours 17 minutes

2 hours 40 minutes + 2 hours 45 minutes = 4 hours 85 minutes = 5 hours 25 minutes

That 5 hours 17 minutes < 5 hours 25 minutes.

So: 26 hours 25 minutes: 5 < 2 hours 40 minutes + 2 hours 45 minutes.

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