3B Mathematics Ch.7 Percentage

3B Mathematics Ch.7 Percentage

By Wang Kwong

Important Formulas!

1. Change = New value - Original value

2. ​Percentage change = (New value - Original value) / Original value x 100%

3. New value = Original value x (1 + Percentage change)​

Subject | Mathematics

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Example

Find the percentage change when a value changes from 156 to 195.

156 is an original value or a new value?

195 is an original value or a new value?

Which formula do we ​need?

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Example

Find the percentage change when a value changes from 156 to 195.

156 is an original value.

195 is a new value.

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Percentage change

= (New value - Original value) / Original value x 100%

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Continuous percentage change

Kay’s weight was 75 kg in March. Her weight decreased by 4% in April, then increased by 5% in May. Find Kay’s weight in May.

Subject | Maths

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Continuous percentage change

Kay’s weight was 75 kg in March. Her weight decreased by 4% in April, then increased by 5% in May. Find Kay’s weight in May.

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x Weight in May = 75 x (1 - 4% + 5%)​

√​ Weight in May = 75 x (1 - 4%) x (1 + 5%)

*​ (1 - 4%) and (1 + 5%) are decay and growth factor

Subject | Maths

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Continuous percentage change

New value = Original value x (1 + r₁%) x (1 + r₂%) x (1 + r₃%) x ...

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if r₁% = r₂% = r₃% = ... = r%?

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​New value = Original value x (1 + r%)ⁿ

Subject | Subject

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