## Introduction

Calculating percentages is an important skill in everyday life. Whether you’re calculating a tip at a restaurant or determining the discount on a sale item, understanding how to work with percentages is crucial. In this article, we’ll explore the question of “21 is what percent of 30” and provide a step-by-step guide to finding the answer.

## Understanding Percentages

Before we dive into the specifics of calculating percentages, it’s important to understand what percentages represent. A percentage is a way of expressing a portion of a whole as a fraction of 100. For example, 50% means “50 out of 100.”

When we talk about “21 is what percent of 30,” we’re essentially asking what fraction of 30 is equal to 21. To find the answer, we need to convert the fraction to a percentage.

## Step-by-Step Guide

Here’s a step-by-step guide to finding the percentage of 21 out of 30:

### Step 1: Divide 21 by 30

To find the fraction of 21 out of 30, we need to divide 21 by 30. This gives us the answer of 0.7.

### Step 2: Multiply by 100

To convert the fraction to a percentage, we need to multiply by 100. This gives us the answer of 70.

### Step 3: Add the Percent Symbol

To express the answer as a percentage, we need to add the percent symbol. The final answer is: 21 is 70% of 30.

## Why Percentages Matter

Percentages are used in a wide range of applications, from calculating discounts to analyzing data. In the business world, percentages are often used to measure growth or decline in sales, revenue, or profits. In personal finance, percentages are used to calculate interest rates on loans or investments. Understanding percentages is also important in science and medicine, where percentages are used to express the effectiveness of treatments or the prevalence of diseases.

## Common Mistakes to Avoid

When working with percentages, there are a few common mistakes to avoid:

### Mistake 1: Forgetting to Divide

One common mistake is forgetting to divide the numerator by the denominator when calculating a fraction. This can result in an incorrect answer when converting to a percentage.

### Mistake 2: Confusing Percentages and Decimals

Another common mistake is confusing percentages and decimals. Percentages are always expressed as a fraction out of 100, while decimals are expressed as a fraction out of 1.

### Mistake 3: Rounding Too Soon

Finally, rounding too soon can also result in an incorrect answer. It’s important to carry out calculations to several decimal places before rounding to the nearest whole number.

## Conclusion

Calculating percentages is an important skill that can be applied in many different areas of life. By understanding the basics of percentages and avoiding common mistakes, you can ensure that your calculations are accurate and reliable. And now, armed with the knowledge of how to calculate “21 is what percent of 30,” you can confidently tackle any percentage-related problem that comes your way.