Science

# How to Calculate Percentages: Formulas and Sample Questions

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How do you calculate percent or percentage (%) in mathematics? Before entering into this discussion, it’s good we know first what is percent / percentage.

Percentage is a number or ratio (ratio) to express the fraction of one hundred indicated by the% symbol. In other words, a percentage is a part of the whole expressed in percentages.

Another opinion says that the definition of percentage is a way to express a number as part of a whole, where the whole is written with 100%.

For example, there are 40 students in one class, 10 of whom are wearing glasses and the remaining 30 students without glasses. Then the percentage of students without glasses is 30 out of 40 = (30/40) x 100% = 0.75 x 100% = 75%. While the percentage of students with glasses is 10 out of 40 = (10/40) x 100% = 0.25 x100% = 25%.

## Formula for Calculating Percentage

We have previously mentioned that to calculate percentages, we must look at a whole as 100%. For example, all students in one class have 40 students, then 40 students = 100%.

Formula for Calculating Percent

Percentage = (Number of Parts / Total Amount) x 100%

With this formula, we can replace fractions or ratios into percentages. With the same formula, we can also change the form of percent to a particular fraction or vice versa.

In addition, we can also change the decimal form, mixed fraction shape, and other forms that allow it to be in the form of percent.

## Example Problem Calculating Percent

To better understand how to find percent, please listen to the discussion through the following sample problems:

### 1. Example Questions on How to Find Percentages

In a teapot, there is 500 ml of orange juice, then 50 ml of orange juice is added to the teapot. The question is, what percentage of the total increase in the volume of orange juice in the teapot?

Discussion:

The percentage increase in the volume of orange juice in the pitcher can be calculated by the formula (Number of Parts / Total Amount) x 100%.

Then the percentage increase in the volume of orange juice in the teapot is
(50ml / 500ml) x 100% = 10%

### 2. Examples of Questions on How to Calculate Percent

An electronics store sells the latest Flat TV for IDR 4,000,000 with a discount offer of 10%. The question is, how do you find the value of 10% of IDR 4,000,000, and what is the price of the Flat TV after the discount is deducted?

Discussion:

Discount value = (percent discount) x (TV price)
Value of discount = (10/100) x Rp 4,000,000
Value of discount = IDR 400,000

Then the price of a Flat TV after the discount is deducted
(Rp.4,000,000) – (Rp.400,000) = Rp3,600,000

### 3. Examples of Problems Calculating Percentage of Interest

Pak Joko saved his money in a bank in the amount of Rp 100,000,000. Every month Pak Joko gets an interest of 0.4% of the value of his savings. The question is, what is the interest rate given by the Bank to Mr. Joko every month?

Discussion:

Bank Interest Value = (Total savings) x percent interest
Value of Bank Interest = (IDR 100,000,000) x (0.4 / 100)
Value of Bank Interest = Rp 100,000,000 x 0.004
Bank Interest Value = IDR 400,000 per month

### 4. Examples of Questions on How to Calculate Percent

Pak Bowo bought a new motorcycle for Rp. 18,000,000 by installments where the down payment was Rp. 2,700,000. The question is, what is the percentage of the down payment (DP) for the purchase of the motorbike?

Discussion:

Percent DP = (DP Price / Motorcycle Price) x 100%
Percent DP = (2,700,000 / Rp. 18,000,000) x 100%
Percent DP = 0.15 x 100%
Percent DP = 15% of the price of a motorcycle

### 5. Example Questions on How to Calculate Percent

The data states that in city A there are 25% of its citizens who work as laborers. If it is known that the number of workers in city A is 150 people, what is the total number of citizens in city A?

Discussion:

Total population = (number of laborers / percentage of laborers) x 100%
Total residents = (150/25%) x 100%
Total citizens = 600

So the total of all citizens in city A is 600 people.

For the record, how to calculate percent as above can be done using a calculator or also with Microsoft Excel.