パーセントの紹介 - 楽しい数学

Introduction to Percents Percents (%) When we say "Percent" we are really saying "per 100" One percent ( 1% ) means 1 per 100. 1% of this line is shaded green: it is very small isn't it? Percents help us understand numbers in comparison to 100. This is useful for many real-world applications like sales and statistics. 50% means 50 per 100 (50% of this box is green) 25% means 25 per 100 (25% of this box is green) Try it Yourself: numbers/images/ani-pct.js Examples: 100% means all Example: 100% of 80 is 100 100 × 80 = 80 50% means half Example: 50% of 80 is 50 100 × 80 = 40 5% means 5 100 ths Example: 5% of 80 is 5 100 × 80 = 4 Using Percent numbers/images/percentage.js Use the slider and try some different numbers (What is 40% of 80? What is 10% of 200? What is 90% of 10?) Because "Percent" means "per 100" think: "this should be divided by 100" So 75% really means 75 100 And 100% is 100 100 , or exactly 1 (100% of any number is just the number, unchanged) And 200% is 200 100 , or exactly 2 (200% of any number is twice the number) A Percent can also be expressed as a Decimal or a Fraction A Half can be written... As a percentage: 50% As a decimal: 0.5 As a fraction: 1 2 Read more about this at Decimals, Fractions and Percentages . Some Worked Examples Example: Calculate 25% of 80 25% = 25 100 And 25 100 × 80 = 20 So 25% of 80 is 20 Example: 15% of 200 apples are bad. How many apples are bad? 15% = 15 100 And 15 100 × 200 = 15 × 200 100 = 15 × 2 = 30 apples 30 apples are bad Example: if only 10 of the 200 apples are bad, what percent is that? As a fraction, 10 200 = 0.05 As a percentage it is: 10 200 x 100 = 5% 5% of those apples are bad Example: Imagine your favorite skateboard is reduced 25% in price. The old price was $120. Find the new price. First, find 25% of $120: 25% = 25 100 And 25 100 × $120 = $30 25% of $120 is $30 So the reduction is $30 Take the reduction from the original price $120 − $30 = $90 The Price of the Skateboard in the sale is $90 Calculation Trick This little rule can make some calculations easier: x% of y = y% of x Example: 8% of 50 Switching the numbers makes the math easier. 8% of 50 is the same as 50% of 8 And 50% of 8 is 4 So 8% of 50 is also 4 The Word "Percent" comes from the latin Per Centum . The latin word Centum means 100, for example a Century is 100 years. Percent vs Percentage My Dictionary says "Percentage" is the "result obtained by multiplying a quantity by a percent". So 10 percent of 50 apples is 5 apples: the 5 apples is the percentage . But in practice people use both words the same way. 877,878,879, 1301, 1302,880, 1303, 1304, 3501, 3502 Percentage Calculator Percentage Difference Percentage Points Decimals, Fractions and Percentages Introduction to Fractions Introduction to Decimals Percents Index Copyright © 2025 Rod Pierce