Some types of math problems learned

### 1.1. Knowledge to remember

- Find the average number.
- Find two numbers whose sum and difference are the same.
- Find two numbers whose sum and ratio are the same.
- Find the difference of two numbers and their ratio.
- The problem is related to unit withdrawal.
- The problem of percentages.
- The problem of uniform motion.
- The problem has geometric content (perimeter, area, volume).

### 1.2. Solving textbook exercises page 170

**Lesson 1 Textbook page 170**

A person rides a bicycle in 3 hours, the first hour covers 12km, the second hour 18km, the third hour covers half the distance traveled in the first two hours. On average, how many kilometers does that person walk per hour?

*Solution guide:*

The distance covered by the cyclist in the third hour is:

(12 + 18) : 2 = 15 (km)

The average distance traveled by a cyclist per hour is:

(12 + 18 +15) : 3 = 15 (km)

Answer: 15km.

Lesson 2 Textbook page 170

A rectangular plot of land has a perimeter of 120m. The length is 10m more than the width. Calculate the area of land.

*Solution guide:*

Half the perimeter of the rectangular plot is:

120 : 2 = 60 (m)

We have a diagram:

The length of the rectangular plot is:

(60 + 10) : 2 = 35 (m)

The width of the rectangular plot is:

60 – 35 = 25 (m)

The area of that land is:

35 x 25 = 875 (m^{2})

Answer: 875m^{2}

Lesson 3 Textbook page 170

A block of metal has a volume of 3.2cm^{3} and weighs 22.4g. A block of metal of the same substance has a volume of 4.5 cm^{3} weight how many grams?

*Solution guide:*

1cm^{3} The number of grams of heavy metal is:

22.4 : 3.2 = 7(g)

4.5cm^{3} The number of grams of heavy metal is:

7 × 4.5 = 31.5(g)

Answer: 31.5g

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