What is 20 of 9? Discover the Secret Math Trick to Solve it Quickly!

Have you ever been in a situation where you need to calculate percentages in a matter of seconds? If you are looking for a quick way to solve math problems such as “What is 20% of 9?” Look no further! In this article, I will teach you a secret math trick that will help you make these calculations quickly and easily.

The Basic Concept of Percentage

The concept of percentage is used extensively in mathematics, accounting, and finance. It is a way of representing a value as a fraction of 100. For example, 20% means 20 out of 100, or 0.2 as a decimal. By knowing the basic concept of percentage, you can solve any percentage problems easily.

The Secret Math Trick: Multiply and Divide by 10

When you are asked to find out 20% of 9, you can use a secret trick: multiply and divide by 10. This trick is an easy way to convert percentages to decimal form and back again, making the calculation much more manageable.

Multiply by 10

The first step is to multiply the percentage by 10. In this case, we are calculating 20% of 9, so we would multiply 20 by 10 to get 200.

Divide by 10

Next, divide the result by 10. This will give you the answer in decimal form. Continuing the same example, divide 200 by 10 to get the answer, which is 20.

The Formula to Solve any Percentage Problem

Now that you know the trick to solve 20% of 9 quickly, let’s look at the formula for any percentage problem:

X% of Y = (X/100) * Y

This formula can be used to find out any percentage of a given number. X represents the percentage and Y represents the value.

Let’s use the formula and solve few examples.

Example 1:

What is 50% of 30?

  • Step 1: Multiply 50 by 10. 50 x 10 = 500
  • Step 2: Divide 500 by 10. 500/10 = 50

Using the formula, (50 / 100) * 30 = 15. Therefore, 50% of 30 is 15.

Example 2:

What is 25% of 80?

  • Step 1: Multiply 25 by 10. 25 x 10 = 250
  • Step 2: Divide 250 by 10. 250/10 = 25

Using the formula, (25 / 100) * 80 = 20. Therefore, 25% of 80 is 20.

How to Solve Multi-Step Percentage Problems?

Some problems require multiple steps to calculate percentages. In these cases, you can use the formula above and solve each step separately.

Example 3:

If a 12% sales tax is added to a $35 item, what is the total amount of the bill?

  • Step 1: Convert 12% to decimal form. 12/100 = 0.12
  • Step 2: Find the amount of sales tax. 0.12 * 35 = 4.2
  • Step 3: Add the amount of the bill to the sales tax. 35 + 4.2 = 39.2

Therefore, the total amount of the bill is $39.20

Tips for Quick Percentage Calculations

Here are some quick tips to help you solve complex percentage problems in seconds:

  • Memorize common percentages, such as 10%, 25%, 50%, and 75%
  • Use a calculator app on your phone or computer for more challenging problems
  • Break down the problem into smaller, more manageable parts.

In Conclusion

Percentages are an essential concept in mathematics, finance, and many other fields. Knowing the secret trick to quickly solve percentage problems can save you time and help you make key decisions faster. With practice, you can master this trick and become a math wiz!

List of Common Questions and Their Answers

  • Q: What is percentage?
  • A: Percentage is a way of representing a value as a fraction of 100.
  • Q: How do you calculate percentages?
  • A: To calculate a percentage, multiply the percentage by the value, and then divide the product by 100.
  • Q: What is the formula for percentage?
  • A: The formula for percentage is: (percentage / 100) * value
  • Q: How do you solve multi-step percentage problems?
  • A: Break down the problem into smaller, more manageable parts and use the formula (percentage / 100) * value to solve each step.


1. “Percentages – mathsteacher.com.au.” Math is Fun – Maths Resources, Math Worksheets, Math Games and More! Accessed 22 June 2021. https://www.mathsisfun.com/percentage.html

2. “What Percentage Is a Fraction? (with pictures) – wiseGEEK.” WiseGEEK: clear answers for common questions, Accessed 22 June 2021. https://www.wisegeek.com/what-percentage-is-a-fraction.htm

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