2TH §7.1 from percentage to factor

• Wiskunde
• Middelbare school
• havo, vwo
• Leerjaar 2

Welcome ...

Plan for today: §7.1 From percentage to factor

Learning goals: 

How to use a factor when calculating percentages

§7.1 

The following slides are about:

+ from percentage to factor

30% of 570 pupils are?

A factor

1. is a number you add
2. is a building where goods are made
3. is a number you multiply by
4. is a percentage

Factor

Instead of using a ratio table where you go to 1 first, you can use the factor to calculate your answer with one calculation.

Factor

The definition of the factor is the number you multiply an original amount by, to get the new amount:

(original = old)

This rule can also be written like this:

Let's go to work

+  §7.1 Do exercises 4 and 6

If you are done, already start with the homework: S4, 7, 8, S9, 9 

Calculating 40 % of 30 % of 300 litres
means ...

1. taking 70 % of 300 litres
2. 0.4 + 0.3 x 300 litres
3. 0.7 x 300 litres
4. 0.4 x 0.3 x 300 litres

40 % of 30 % of 300 litres
is ....

1. 48 litres
2. 46 litres
3. 36 litres
4. 38 litres

In the next slide first an increase and then a decrease. 

Watch carefully how to tackle this more complicated job!

Percentage of a percentage

Using a factor is useful when an amount changes by a given percentage and is then again changed by a given percentage.

A company increases the price of their 400 euro tv by 12% and then give a discount of 20% on the new price.

Question 1: What is the sale price of the tv?

Percentage of a percentage

A company increases the price of their 400 euro tv by 12% and then gives a discount of 20% on the new price.

Question 1: What is the sale price of the tv?        

Percentage of a percentage

Using a factor is useful when an amount changes by a given percentage and is then again changed by a given percentage.

A company increases the price of their 400 euro tv by 12% and then give a discount of 20% on the new price.

Question 2: What percentage is the actual discount?

Percentage of a percentage

A company increases the price of their 400 euro tv by 12% and then gives a discount of 20% on the new price.

Question 2: What percentage is the actual discount?

Homework

+  §7.1 Do exercises S4, 7, 8, S9, 9 

+  Check your answers with the Solutionsbook and upload your work in Classroom