1-3 Percentage increase and decrease (p. 14)

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• Leerjaar 3

1-3 Percentage increase and 

decrease (p. 14)

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• Determine the factor when there is exponential growth.
• Determine the formula if you have the table for exponential growth between two variables.

• Make calculations based on a percentage increase or a percentage decrease.
• Calculate the percentage of a percentage.

Percentage increase or percentage decrease

- If an ammount decreases by 15%, you can calculate the new ammount by multiplying by the factor 0,85.

- If an ammount increases 

by 30%, you can calculate

 the new amount by 

multiplying with the 

factor 1,30.

16 (p. 14)

A

B

C

D

E

A

1. 1,12
2. 0,96
3. 1,55
4. 0,69

B

1. 280
2. 1 372,80
3. 7,44
4. 322,23

C

1. 4,80
2. 467
3. 61
4. 3,20

D

1. 280
2. 612
3. 322
4. 344

E

1. 61
2. 135
3. 54
4. 141

Percentage of a percentage

1. Write both percentages as factors.

2. Multiply the two factors by 

     eacht other.

3. Use this factor to calculate 

    the required percentage.

19 (p. 15)

19 a

1. 1,0028%
2. 28%
3. 2,8%
4. 0,28%

19 b

1. 0,9%
2. 9%
3. 8%
4. 0,8%

19 c

1. 0,9%
2. 9%
3. 8%
4. 0,8%

20 (p. 15)

Conclusion:

• Calculations based on percentage must first be convertedinto a factor.
• Calculating a percentage of a percentage:

1. Write both percentages as factors
2. Multiply the two factors by each other
3. Use this factor to calcualte the required 

        percentage

Try on your own

1, 2, 5 and 7

TRY ON YOUR OWN

15, 17, 18, 21, 22 (p. 14)

RULES:

• In your writingbook
• Use: Textbook
• Discussion when you are stuck is allowed

Extra excercise: B5, B6 (p. 27)

Challenge: C3 (p. 30)