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# How do you calculate percentages

In math, a percentage is a way of writing a number as a fraction of 100 (per cent means per hundred). For example, if you hear that 40% of people own a pet this means that 40 out of 100 people own a pet. Many people ask ‘how do you calculate percentages’? This post will answer that question and give you a few examples to help you along.

How do you calculate percentage

Example 1: Converting Decimals

Many basic percentage problem require you to convert a decimal to a percentage. To do this, simply multiply the decimal by 100. This moves the decimal point two places to the right. Here are two examples of how to do this…

Question:

Convert 0.45 to a percentage

Multiply 0.45 by 100 (0.45 x 100)

The answer is 45 (move the decimal place to the right 2 places). Therefore, 0.45 is 45%.

Question:

Convert 0.657 to a percentage

0.657 x 100 = 65.7 (moving the decimal point to the right 2 places)

Therefore, 0.657 is 65.7%

Example 2: What percentage of…

This is best illustrated by a couple of examples.

Question:

In a park, Bob observed that 20 out of 50 dogs have brown hair. What percentage of dogs had brown hair?

First, divide 20 by 50: 20/50 = 2/5 = 0.40

Next, multiply the answer by 100 (remember, just move the decimal point two places to the right).

0.40 x 100 = 40

Question:

Bob was sitting by the road one day and observed that 30 out of 120 cars were black. Find the percentage of cars that were NOT black.

You want the cars that were not black. If 30 out of 120 cars were black, how many cars were not black?

Well, 120 – 30 = 90.

Therefore, 90 out of 120 cars are not black.

First, do 90/120 = 9/12 = 3/4 = 0.75

0.75 x 100 = 75

So 75% of the cars were not black.

Example 3: Percentage Increases

Again, I will illustrate by example.

Question:

The price of a \$2.00 soft drink was increased to \$2.40. Find the percentage increase.

First, find the difference in price:

2.40 – 2.00 = 0.40

Next, divide 0.40 by 2.00

0.40/2.00 = 1/5 = 0.20

Now, convert the decimal to a percentage by multiplying by 100.

0.20 x 100 = 20 (move the decimal 2 places to the right!)

Therefore, the price has increased by 20%.

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