Percentage

### 1.1. Knowledge to remember

**a)** **For example:** Van Tho primary school has 600 students, including 315 girls. Find the percentage of the total number of students and the number of students in the whole school.

The ratio of female students to the number of students in the whole school is 315 : 600

We have: 315 : 600 = 0.525

0.525 x 100 : 100 = 52.5 : 100 = 52.5%

So the ratio of the number of female students to the total number of students is 52.5%.

Usually we write the calculation as follows:

315 : 600 = 0.525 = 52.5%

*** To find the percentage of two numbers 315 and 600 we do the following:

- Find the quotient of 315 and 600.
- Multiply that quotient by 100 and add the % symbol to the right of the product found.

**b)** Problem: In 80kg of sea water, there are 2.8kg of salt. Find the percentage of salt in seawater.

**Solution:**

The percentage of salt in seawater is:

2.8 : 80 = 0.035

0.035 = 3.5%

Answer: 3.5%

### 1.2. Solve textbook exercises on page 74

**Lesson 1 of the textbook page 74:**

Write in the form:

\(\frac{{75}}{{300}};\frac{{60}}{{400}};\frac{{60}}{{500}};\frac{{96}}{{) 300}}\)

Pattern: \(\frac{{75}}{{300}} = \frac{{25}}{{100}} = 25\% \)

**Solution guide:**

\(\begin{array}{l}

\frac{{60}}{{400}} = \frac{{15}}{{100}} = 15\% \\

\frac{{60}}{{500}} = \frac{{12}}{{100}} = 12\% \\

\frac{{96}}{{300}} = \frac{{32}}{{100}} = 32\%

\end{array}\)

Lesson 2 Textbook page 74:

Inspecting a factory’s products, it was found that on average, 95 out of every 100 products met standards. What percentage of the factory’s total products is the number of qualified products?

*Solution guide:*

The number of qualified products as a percentage of the factory’s total products is:

\(\frac{{95}}{{100}} = 95\% \)

Answer: 95%

Lesson 3 Textbook page 74:

An orchard has 1000 trees, of which 540 are for timber and the rest are fruit trees.

a) What is the percentage of trees in the garden?

b) What is the percentage ratio between the number of fruit trees and the number of trees in the garden?

*Solution guide:*

a) The ratio of the number of trees for timber and the number of trees in the garden is:

\(\frac{{54}}{{1000}} = \frac{{54}}{{100}} = 54\% \)

b) The number of fruit trees in the garden is:

1000 − 540 = 460 (tree)

The ratio of the number of fruit trees to the number of trees in the garden is:

\(\frac{{46}}{{1000}} = \frac{{46}}{{100}} = 46\% \)

Answer: a) 54%

b) 46%.

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