Study Guide

Ratios & Percentages - Percents

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A percent is just a fraction or ratio with a nice, easy denominator of 100.

We see percents everywhere: shopping, grades, weather forecasts, sports statistics. Like fractions and decimals, percentages are ways of expressing parts of a whole.

For example, 50% (or "fifty percent") just means 50 out of 100 parts, or  50/100 = 1/2. That's why a 50% grade on a math test means we only got half of the answers right. Yeesh, better study harder next time.

To tell the truth, we probably could get by on fractions and decimals alone. But percents are friendly, helpful, attractive, and memorable. We kind of have a crush on percents. Out of 100 is a really simple proportion to deal with. Think of a dollar bill: it's really 100 pennies. Half a dollar is 50 cents, or 50% of the whole dollar.

Visualizing Percentages

When we work with percentages, it's important to be able to imagine what they look like. The easiest way to do this is to convert them into fractions. All we need to remember is that a percent is just a fraction with a denominator of 100.

Here are some of the most common percents. Notice they can also be written as equal ratios, or proportions.

50% pie chart

25% pie chart

75% pie chart

20% pie chart

33.3% pie chart

66.6% pie chart

10% pie chart

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