Calculate 42% of 15: Step-by-Step Percentage Solution

Percentage Calculations with Fraction Conversion

Calculate 42% of 15:

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:03 Let's find 42% of 15.
00:07 First, change 42% into a fraction.
00:14 So, 42% becomes forty-two over one hundred.
00:25 Now, multiply this fraction by 15.
00:34 Break it down and simplify the fractions.
00:50 And that's the solution!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Calculate 42% of 15:

2

Step-by-step solution

To solve the exercise, will begin by converting the percentage into a fraction:

42%=42100 42\%=\frac{42}{100}

We will then proceed to multiply the fraction by 15

15×42100= 15\times\frac{42}{100}=

In order to simplify this operation let's break down the 15 from the multiplication exercise as well as the 100 in the denominator for the multiplication exercise:

3×5×425×20 3\times5\times\frac{42}{5\times20}

Take note that the five in both exercises can be reduced:

3×4220=3×(2×21)2×10 3\times\frac{42}{20}=\frac{3\times(2\times21)}{2\times10}

Furthermore we can also reduce the 2 in the numerator and the denominator:

3×2110=6310=6.3 \frac{3\times21}{10}=\frac{63}{10}=6.3

3

Final Answer

6.3

Key Points to Remember

Essential concepts to master this topic
  • Rule: Convert percent to fraction by dividing by 100
  • Technique: Simplify before multiplying: 15×42100=3×4220 15\times\frac{42}{100} = 3\times\frac{42}{20}
  • Check: Verify 6.3 is 42% of 15 by calculating 6.315=0.42 \frac{6.3}{15} = 0.42

Common Mistakes

Avoid these frequent errors
  • Forgetting to convert percentage to decimal or fraction
    Don't multiply 15 × 42 = 630! This ignores that 42% means 42 per hundred, not 42 whole units. Always convert 42% to 0.42 or 42100 \frac{42}{100} first.

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 need to convert 42% to a fraction first?

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Because 42% means "42 out of 100" or 42100 \frac{42}{100} . You can't just multiply 15 × 42 because that would give you 42 whole units, not 42 percent!

Can I just multiply 15 × 0.42 instead?

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Absolutely! Converting 42% to 0.42 is often easier: 15 × 0.42 = 6.3. Both the fraction method and decimal method give the same answer.

Why did the solution break down 15 and 100 into smaller factors?

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Breaking down numbers helps you cancel common factors and simplify calculations. Since 15 = 3 × 5 and 100 = 5 × 20, you can cancel the 5's to make the math easier!

How can I check if 6.3 is really 42% of 15?

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Divide your answer by the original number: 6.315=0.42 \frac{6.3}{15} = 0.42 . Since 0.42 = 42%, your answer is correct! This reverse check always works.

What if I get a different decimal answer?

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Double-check your arithmetic! Common errors include forgetting to convert the percentage or making calculation mistakes. Remember: 42% of any number should be less than half that number.

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