Solve Fraction Addition: 2/3 + 7/9 Step-by-Step

Fraction Addition with Common Denominators

23+79= \frac{2}{3}+\frac{7}{9}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 We want to find the least common denominator
00:06 Multiply by 3 to find the common denominator
00:09 Remember to multiply both numerator and denominator
00:17 Calculate the multiplications
00:23 Add under the common denominator
00:28 Calculate the numerator
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

23+79= \frac{2}{3}+\frac{7}{9}=

2

Step-by-step solution

To solve this problem, we will perform the following steps:

  • Step 1: Find the Least Common Multiple (LCM) of the denominators 3 and 9.
  • Step 2: Convert both fractions to have a common denominator.
  • Step 3: Add the numerators of the converted fractions and write the result over the common denominator.
  • Step 4: Simplify the resultant fraction if needed.

Let's work through each step:

Step 1:
The denominators of our fractions are 3 and 9. The LCM of 3 and 9 is 9, since 9 is the smallest number that both 3 and 9 divide evenly into.

Step 2:
Convert each fraction to have a denominator of 9.

- For 23 \frac{2}{3} , multiply both the numerator and denominator by 3 (because 93=3 \frac{9}{3} = 3 ):
23=2×33×3=69 \frac{2}{3} = \frac{2 \times 3}{3 \times 3} = \frac{6}{9}

- The second fraction 79 \frac{7}{9} already has a denominator of 9, so it remains the same:
79 \frac{7}{9}

Step 3:
Add the two fractions:
69+79=6+79=139 \frac{6}{9} + \frac{7}{9} = \frac{6 + 7}{9} = \frac{13}{9}

Step 4:
The fraction 139 \frac{13}{9} is in its simplest form because 13 is a prime number and does not divide evenly into 9.

Therefore, the solution to the problem is 139 \frac{13}{9} .

3

Final Answer

139 \frac{13}{9}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Find LCM of denominators to create common denominators
  • Technique: Convert 23 \frac{2}{3} to 69 \frac{6}{9} by multiplying by 3
  • Check: Verify 69+79=139 \frac{6}{9} + \frac{7}{9} = \frac{13}{9} is in simplest form ✓

Common Mistakes

Avoid these frequent errors
  • Adding numerators and denominators separately
    Don't add 2+7=9 and 3+9=12 to get 912 \frac{9}{12} ! This creates a meaningless fraction that doesn't represent the actual sum. Always find a common denominator first, then add only the numerators.

Practice Quiz

Test your knowledge with interactive questions

Complete the following exercise:

\( \frac{3}{4}:\frac{5}{6}=\text{?} \)

FAQ

Everything you need to know about this question

Why can't I just add the numerators and denominators separately?

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Fractions represent parts of a whole. You can only add fractions when they represent parts of the same size whole (same denominator). Adding numerators and denominators separately doesn't follow fraction rules.

How do I know if 9 is the right common denominator?

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Since 9 is a multiple of 3 (9 ÷ 3 = 3), it works as a common denominator. The LCM of 3 and 9 is 9 because it's the smallest number both denominators divide into evenly.

Is 139 \frac{13}{9} really in simplest form?

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Yes! To simplify, we need a common factor between 13 and 9. Since 13 is prime and doesn't divide 9, the fraction 139 \frac{13}{9} cannot be reduced further.

Can I convert this to a mixed number?

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Absolutely! 139=149 \frac{13}{9} = 1\frac{4}{9} because 13 ÷ 9 = 1 remainder 4. Both forms are correct - use whichever your teacher prefers!

What if the denominators were larger numbers?

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The same process works! Find the LCM of the denominators, convert both fractions, then add. For example, with denominators 12 and 8, you'd find LCM = 24.

Do I always need to find the LCM, or can I use any common multiple?

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You can use any common multiple, but the LCM makes calculations easier with smaller numbers. Using a larger common multiple just means more work simplifying at the end.

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