The importance of learning something is knowing how to apply it in your daily life. Some of us might not have been fans of mathematics or numbers in school. However, in real life situation, you are faced with numbers every day. Being able to do a few mathematical calculations can prove to be very helpful. For instance, your creditor might be trying to explain to you the percentage and rates of the loan, but if you don't remember or know how to calculate percentage increase or decrease all that will be irrelevant. Percentage calculations are also necessary when checking interest rates; allowance rises, discounts on sales, pay increases, etc.
Percentage (represented by the symbol %) refers to “out of 100” or “for every 100”. It is the mathematical representation of a number as a whole out of 100. The phrase "percent" in English originates from an Italian word per cento or the French word pour cent; the two words share the same meaning: per hundred. Percentages can be written in two ways using the % symbol or in decimal form.
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How to calculate percentage of a number
When calculating percentages, it can either be a percentage representation of the whole number or a percentage representation of an increase or decrease of the whole amount.
So what is the mathematical formula of how to calculate percentage of an amount?
- Start by determining the mathematical value of the whole, for example, 84 children.
- Then find the value that you want it to represent in percentage form. (48 are girls, 36 are boys).
- To find the percentage of boys or girls we use the following formula.
(Number of girls/ boys ÷ total number of children) × 100
For girls: (48 ÷ 84) × 100 = 57.143%
For boys: (36 ÷ 84) × 100 = 42.857%
How to calculate the percentage increase
If you are calculating the percentage increase or decrease, you will need to work out the difference (increase or decrease) of the first amount. After that divide the increase by the original amount and finally multiply by 100. The amount you get will be your percentage increase or decrease.
- Start by working out the difference between the two numbers, subtract the second value (new number) from the first value (original number).
- Increase = New Number - Original Number
- Then divide the value of the increase by the original number and multiply the answer by 100.
% Increase = Increase ÷ Original Number × 100.
If your answer is a negative number, then this is a percentage decrease.
Example: In January Dylan had 35 cows, in February he had 45 cows, by what percentage did Dylan’s cows increase in February?
Increase: 45 - 35 cows = 10 cows
% Increase: (10 ÷ 35) × 100 = 28.57%
How to calculate percentage decrease
- First, work out the difference by subtracting the two numbers you are comparing.
Decrease = Original Number - New Number
- Then divide the reduction by the original number and multiply the answer by 100.
% Decrease = Decrease ÷ Original Number × 100
If your answer is a negative number, then this is a percentage increase.
Example: In January Dylan had 45 cows, in February he had 35 cows, by what percentage did Dylan’s cows decrease in February?
Decrease: 45 - 35 cows = 10 cows
% Decrease: (10 ÷ 45) × 100 = 22.22%
If you are looking for a formula of how to calculate the percentage of amount, then the first formula will be beneficial.