# How to work out a percentage of a number, percentage change, difference

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Percentage calculation plays a fundamental action in many aspects of our life. For instance, you sometime want to how to work out a percentage of a number to know banking interests or the discount of many different things. Moreover, percentage calculation is important for various business, professional fields such as academic studies, the rise of population and so on,…

## What is the define of percentage?

Percentage, which can also be referred as percent, is a fraction of a number out of 100%. Percentage means “per 100” and indicates a piece of the total amount. For example, 45% will represent 45 out of 100, or 45% of the total amount.

Percentage may also be known as “out of 100” or “for every 100.” Therefore, you could say either “it snowed 20 days out of every 100 days” or “it snowed 20% of the time.”

The percentage can also be written in several ways. One way is that to portray it as a decimal. For example, 24% could also be written as 0.24. You can find the decimal version of a percentage by dividing it by 100. ## 2. How to work out a percentage of a number?

The following formula is a common one to work out a percentage:

### Determining the total amount of what you want to calculate a percentage

Typically, if you want to calculate the percentage of the days which rained in a month, you will use the number of days in that month as the total amount. So, let’s try that we are evaluating the amount of rain during the month of April’s 30 days.

### Dividing the number to determine the percentage of a number

Continue the example above, let’s say that it only rained 15 of the 30 days in April. You divide 15 by 30, which equals 0.5.

### Multiply that above value by 100

Continuing with the received example, you will multiply 0.5 by 100. This equals 50, which will give you the answer of 50%. In conclusion, in April, it rained 50% of the time. ## 3. How to work out a percentage change

A percentage change means a mathematical value that denotes the degree of change over time. It is almost used frequently in finance to determine the change in the price of a security on the over time. This formula can be applied to any number that is measured over time.

Besides, it is also equal to the change in a given value. You can solve the percentage change by dividing the whole value by the original value and then multiplying it with 100. The formula to solve the percentage change is following:

• For a price of percentage increase:
[(New Price – Old Price)/Old Price] x 100

• For a price of percentage decrease:
[(Old Price – New Price)/Old Price] x 100

Here’s an example of a percentage increase:

A fridge cost \$100 last year but now it costs \$125. To determine the price increase, you would subtract the old price from the new price, like 125 – 100 = 25. Then you divide this by the old price: 25 divides by 100 which will equal 0.25. Next, multiply this number by 100: 0.25 x 100 = 25, or 25%. So, the fridge price has increased by 25% over the past year.

An example of a percentage decrease:

An air conditioner cost \$100 last year but now it costs only \$75. To determine the price decrease, you would subtract the new price from the old price, such as 100 – 75 = 25. You will divide this number by the old price: 25 divided by 100 equals 0.25. You will then multiply this by 100: 0.25 x 100 = 25. or 25%. This means the air conditioner costs 25% less than it did in the previous year.

## 4. How to calculate the percentage difference

You can use percentage to compare two different items that related to each other. For instance, you want to determine how much a product cost last year comparing with how much a similar product costs this year. This calculation will give you the percent difference between the two product prices.

This is the formula used to calculate a percentage difference:
|V1 – V2|/ [(V1 + V2)/2] × 100

In this formula, V1 is equal to the cost of one product, and V2 is equal to the cost of the other product.

An example of determining the difference between product costs would include:

A product cost \$25 last year and it costs \$30 this year. To determine the percentage difference, first, you would subtract the costs from each other: 30 – 25 = 5. Then, you will determine the average of these two costs (25 + 30 / 2 = 27.5). Then, divide 5 by 27.5 = 0.18. Next, multiply 0.18 by 100 = 18. This means that the cost of that product in this year is 18% which is more than the cost of one in last year.