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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

Answer:

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

Answer

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?

Answer:

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

Therefore, the answer is 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.

Answer:

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.

Answer:

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%.

Other Maths Topics:

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