Calculate 30% of 90: A Hands-On Math Problem

Percentage Calculation with Decimal Conversion

Calculate 30 % of 90:

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:03 Let's find 30 percent of 90.
00:07 First, we'll change 30 percent into a fraction.
00:17 This means 30 over 100.
00:23 Multiply this fraction by 90. That's our next step.
00:39 Simplify the numbers if possible for an easier calculation.
00:52 And there you have it! That's the answer.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Calculate 30 % of 90:

2

Step-by-step solution

To solve this problem, we will determine 30% of 90 using the percentage formula. Here's how we'll do it:

  • Step 1: Identify the necessary formula for the calculation.
  • Step 2: Substitute the values into the formula and compute.
  • Step 3: Verify the result and match it with the answer choices.

Now, let's proceed through these steps:

Step 1: The formula for calculating a percentage of a number is given as:
Percentage Value=(x100)×Total \text{Percentage Value} = \left( \frac{x}{100} \right) \times \text{Total}

Step 2: Substitute the given values into the formula.
Here, x=30 x = 30 and Total=90\text{Total} = 90. Thus, the formula becomes:
Percentage Value=(30100)×90 \text{Percentage Value} = \left( \frac{30}{100} \right) \times 90 .

Step 3: Compute the expression.
First, calculate 30100=0.3\frac{30}{100} = 0.3 .
Then multiply by 90:
0.3×90=27 0.3 \times 90 = 27 .

Therefore, 30% of 90 is 27 27 .

3

Final Answer

27

Key Points to Remember

Essential concepts to master this topic
  • Formula: Percentage = (percent/100) × total value
  • Technique: Convert 30% to 0.3, then multiply: 0.3 × 90 = 27
  • Check: Verify 27 is 30% of 90: 27 ÷ 90 = 0.3 = 30% ✓

Common Mistakes

Avoid these frequent errors
  • Adding percent directly to the number
    Don't add 30 + 90 = 120! This treats the percent as a whole number instead of a fraction. The percent symbol (%) means "out of 100," so 30% = 30/100. Always convert the percent to a decimal first, then multiply.

Practice Quiz

Test your knowledge with interactive questions

Calculate 30 over 100 as a percentage:

FAQ

Everything you need to know about this question

Why do I divide the percent by 100?

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The percent symbol % literally means "out of 100." So 30% is really 30100 \frac{30}{100} , which equals 0.3 as a decimal.

Can I use the percent key on my calculator?

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Yes! Most calculators let you type 30% × 90 directly. The % key automatically converts 30% to 0.3 for you.

What if I get a decimal answer instead of a whole number?

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That's completely normal! Not all percentage calculations result in whole numbers. For example, 33% of 50 = 16.5.

How can I check my answer without a calculator?

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Think of easier percentages: 10% of 90 is 9, so 30% should be 3 times larger than 9, which gives us 27!

Is there a shortcut for calculating percentages?

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For multiples of 10%:

  • 10% of any number: Move decimal point left one place
  • 20% = 2 × 10%, 30% = 3 × 10%, etc.

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