Theory
With percentage decrease, you look at how much has been taken away.
You always compare that decrease with the starting value, because the starting value is 100%.
Divide the decrease by the starting value and then multiply by 100.
- Calculate how much has been taken awaySubtract the new value from the starting value.
When subtracting, you take away an amount or calculate the difference between two numbers.
The first number is the starting number. The second number is what you subtract from it.
Pay attention to whether you cross a ten. Then you need to carefully keep track of the ones and tens separately.
- Compare the decrease with the starting valueUse the decrease as the part and the starting value as the whole.
A percentage compares a part with a whole, where the whole is 100%.
Divide the part by the whole to see what part of the total you have.
Then multiply by 100 and put a percent sign after it.
- Divide by the wholeDivide the part by the whole to see what part of the whole you have.
Dividing means sharing an amount fairly or seeing how many equal groups fit into it.
The first number is the total amount. The second number tells you what you divide by.
Always check whether the division works out exactly. If it does not, you get a decimal number or fraction as the answer.
- Convert to percentMultiply by 100 to write the part as a percentage.
You use multiplication with equal groups.
A × B means that you take the same amount B, A times.Instead of adding again and again, you calculate the product all at once.
- Divide by the whole
- Calculate how much has been taken away60 - 45 = 15.
- Compare the decrease with the starting valueCompare the decrease 15 with the starting value 60.
- Divide by the whole15 ÷ 60 = 0,25.
- Convert to percent0,25 × 100 = 25%.
- Divide by the whole