Compare Fractions 4/7 and 6/9: A Cake-Sharing Problem

Fraction Comparison with Common Denominators

Benjamin ate 47 \frac{4}{7} of a cake and

George ate 69 \frac{6}{9} of the cake.

Who ate the most cake?

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Which fraction is bigger?
00:03 We want to get a common denominator, so we'll multiply each fraction by the other's denominator
00:19 Let's calculate the multiplications
00:28 Now that the denominators are equal, the larger numerator determines
00:32 And this is the solution to the question

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Benjamin ate 47 \frac{4}{7} of a cake and

George ate 69 \frac{6}{9} of the cake.

Who ate the most cake?

2

Step-by-step solution

To solve this problem, we'll compare the fractions representative of the cake portions that Benjamin and George ate.

  • Step 1: Simplify Fractions
    George ate 69 \frac{6}{9} of the cake. Simplifying this fraction, we divide both the numerator and the denominator by their greatest common divisor, which is 3. Thus, 69=23 \frac{6}{9} = \frac{2}{3} .
  • Step 2: Find Common Denominator
    The denominators of the two fractions we are comparing are 7 and 3. The least common multiple (LCM) of 7 and 3 is 21.
  • Step 3: Convert to Common Denominator
    Convert 47 \frac{4}{7} and 23 \frac{2}{3} to fractions with a common denominator of 21:
    - For 47 \frac{4}{7} , multiply the numerator and the denominator by 3: 47=4×37×3=1221 \frac{4}{7} = \frac{4 \times 3}{7 \times 3} = \frac{12}{21} .
    - For 23 \frac{2}{3} , multiply the numerator and the denominator by 7: 23=2×73×7=1421 \frac{2}{3} = \frac{2 \times 7}{3 \times 7} = \frac{14}{21} .
  • Step 4: Compare the Fractions
    Now, compare the numerators: 12 and 14. Since 14 is greater than 12, we can conclude that 1421 \frac{14}{21} (or 23 \frac{2}{3} ) is greater than 1221 \frac{12}{21} (or 47 \frac{4}{7} ).

Therefore, George ate more of the cake.

The correct answer is George.

3

Final Answer

George

Key Points to Remember

Essential concepts to master this topic
  • Simplify: Reduce fractions to lowest terms before comparing
  • Common Denominator: Use LCM: 7 and 3 → 21
  • Check: Convert to same denominator: 1221 \frac{12}{21} vs 1421 \frac{14}{21}

Common Mistakes

Avoid these frequent errors
  • Comparing numerators without common denominators
    Don't compare 4 and 6 directly = wrong conclusion! These numbers represent different-sized pieces, so you can't compare them meaningfully. Always find a common denominator first to make fair comparisons.

Practice Quiz

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What number is marked on the number axis?

000111

FAQ

Everything you need to know about this question

Why can't I just compare 4 and 6 directly?

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Because 4 out of 7 pieces is different from 6 out of 9 pieces! The pieces are different sizes. You need a common denominator to make fair comparisons.

Do I always need to simplify fractions first?

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It's not required, but it's highly recommended! Simplifying makes the numbers smaller and easier to work with. For example, 69 \frac{6}{9} becomes 23 \frac{2}{3} .

What if the denominators are really big numbers?

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Use the same process! Find the LCM of the denominators, then convert both fractions. The math works the same way regardless of the size of the numbers.

Can I use decimals instead of common denominators?

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Yes! Convert both fractions to decimals: 470.571 \frac{4}{7} \approx 0.571 and 230.667 \frac{2}{3} \approx 0.667 . Since 0.667 > 0.571, George ate more.

How do I find the LCM of two numbers?

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List multiples of each number until you find the first one they share. For 7 and 3: 7, 14, 21... and 3, 6, 9, 12, 15, 18, 21... The first match is 21!

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