In another case you want to indicate, for example, how many percent a number has descended or increased. Enter these values at the top of the page, 40 and 20. Move the comma in 800 2 places to the left and you get 8.00. In our calculation, 40/100 * 20 we could also do so: (40 * 20) / 100 (it is the same). A little trick does apply here: if you want to divide by a hundred, just move the comma two places to the left. For example: what is 40% of 20? That's 40 hundredths of 20, so if we share 20 cookies in 100 equal pieces (good luck with that!), 40 of those pieces are our 40% of 20 cookies. Sometimes we want to show the ratio between 2 numbers. That is nice, but we usually do not only use percentages. So 5 percent is the same as 5%, 0.05, 5/100 or five hundredths. We calculate the percentage of blonde students by applying a rule of three (using a table): Recall the above example: in a class of 80 students, 12 are blonde. Therefore, we can calculate the percentage by applying a simple rule of three. This means that the percentage is directly proportional to the ratio. The higher a ratio is, the higher the percentage is. So we find that 15 out of 100 students are blonde, so 15% of the students are blonde. We solve the first-degree equation (the 100 in the denominator passes multiplicatively to the other side): 12 / 80 = x /100 → x = 12 * 100 / 80 → x = 15 Since the ratio must be equal, we set both expressions equal to calculate Since we want to write the ratio relative to 100, we write 100 in the numerator: Note that in the denominator we write the total number of students and in the numerator the number of blonde students. Since there are 12 blonde students out of a total of 80 students, the ratio of blonde students is: R = 12 / 80 We calculate the ratio of blonde students in a class of 80 students, of which 12 are blonde. The percentage n % means n individuals out of 100.ĥ0% is half of the total (50 out of 100).Ģ5% is a quarter of the total (25 out of 100).Ģ0% is one-fifth of the total (20 out of 100). To calculate a percentage, we identify the total number by 100%. Percentage is a way of referring to a ratio by referring to the number 100. Definition and calculation of percentages This example shows the practicality of the widespread use of percentages, which is why we need to be able to understand and calculate percentages.Ģ. Let's look at an example with different ways of describing a ratio:Ģ0 out of 80 British people believe the sun revolves around the earth.Ģ5 out of 100 British households are single-person households.Ĭomparing these ratios might be a bit complicated, but if we write them in terms of percentages, they are equivalent: 25%, which is 25 out of 100. We explain how percentages are calculated and give some examples.
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