Calculate the Percentage of 21 over 225: Step-by-Step Solution

Percentage Calculations with Mixed Number Results

What is the percentage of 21 over 225?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Calculate 21 as a percentage of 225
00:05 Apply the formula for calculating percentages
00:10 Divide one number by the other and proceed to multiply by 100
00:15 Break down 21 into factors of 7 and 3, and 225 into factors of 75 and 3
00:30 Reduce wherever possible
00:40 Break down 75 into factors of 25 and 3, and 100 into factors of 25 and 4
00:55 Reduce wherever possible
01:03 This is the solution

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

What is the percentage of 21 over 225?

2

Step-by-step solution

To find the percentage of 21 over 225, we'll follow these steps:

  • Step 1: Express 21 as a fraction of 225: 21225 \frac{21}{225} .
  • Step 2: Simplify the fraction.
  • Step 3: Convert the simplified fraction into a percentage by multiplying by 100%.

Now, let's work through each step:

Step 1: The initial fraction is 21225 \frac{21}{225} .

Step 2: Simplify the fraction. We find the greatest common divisor (GCD) of 21 and 225, which is 3.

Divide both the numerator and the denominator by 3:

21÷3225÷3=775 \frac{21 \div 3}{225 \div 3} = \frac{7}{75} .

Now the fraction is simplified to 775 \frac{7}{75} .

Step 3: Convert the simplified fraction into a percentage:

Multiply by 100%: 775×100%=70075% \frac{7}{75} \times 100\% = \frac{700}{75}\% .

Simplify 70075 \frac{700}{75} :

700 divided by 75 equals 9 with a remainder of 25. Thus, 70075=92575% \frac{700}{75} = 9 \frac{25}{75}\% .

Simplify 2575 \frac{25}{75} to 13 \frac{1}{3} (since 25 and 75 can be divided by 25).

Therefore, the percentage is 913% 9 \frac{1}{3}\% .

The solution to the problem is 913% 9\frac{1}{3}\% , which corresponds to choice 4.

3

Final Answer

913% 9\frac{1}{3}\%

Key Points to Remember

Essential concepts to master this topic
  • Rule: Convert fraction to percentage by multiplying by 100%
  • Technique: Simplify first: 21225=775 \frac{21}{225} = \frac{7}{75} then multiply by 100
  • Check: 913%=283%=9.33...% 9\frac{1}{3}\% = \frac{28}{3}\% = 9.33...\%

Common Mistakes

Avoid these frequent errors
  • Converting to decimal before simplifying the fraction
    Don't calculate 21 ÷ 225 = 0.0933... first = messy decimals and rounding errors! This makes it harder to get exact mixed number answers. Always simplify the fraction first, then convert to percentage.

Practice Quiz

Test your knowledge with interactive questions

Convert the fraction into a percentage:

\( \frac{2}{100}=\text{?} \)

FAQ

Everything you need to know about this question

Why do I need to simplify the fraction before converting to percentage?

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Simplifying first makes the calculations much easier! Working with 775 \frac{7}{75} instead of 21225 \frac{21}{225} gives you smaller numbers and cleaner final answers.

How do I know when my answer should be a mixed number?

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When your percentage calculation gives you an improper fraction (numerator larger than denominator), convert it to a mixed number. Like 283%=913% \frac{28}{3}\% = 9\frac{1}{3}\% .

What if I can't find the GCD easily?

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Start by checking if both numbers are divisible by small primes like 2, 3, 5. For 21 and 225: both end in digits divisible by 3, so try dividing by 3 first!

Can I just use a calculator to get the decimal answer?

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While calculators give decimal answers, many math problems require exact fractional forms. Practice the fraction method to understand the concept better!

How do I multiply a fraction by 100%?

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Multiply the numerator by 100: 775×100%=7×10075%=70075% \frac{7}{75} \times 100\% = \frac{7 \times 100}{75}\% = \frac{700}{75}\% . Then simplify this new fraction.

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