Solve the Fraction Addition: 1/7 + 1/8 Step-by-Step

Fraction Addition with Common Denominators

17+18= \frac{1}{7}+\frac{1}{8}=

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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 each fraction by the other denominator to find the common denominator
00:09 Remember to multiply both numerator and denominator
00:18 Calculate the multiplications
00:26 Add under the common denominator
00:34 Calculate the numerator
00:37 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

17+18= \frac{1}{7}+\frac{1}{8}=

2

Step-by-step solution

To solve this problem, we'll follow these steps:

  • Step 1: Identify the common denominator.
  • Step 2: Convert each fraction to have this common denominator.
  • Step 3: Add the converted fractions.
  • Step 4: Simplify the result.

Now, let's work through each step:
Step 1: The denominators are 7 and 8. Their product is 7×8=56 7 \times 8 = 56 . So, the common denominator is 56.
Step 2: Convert 17\frac{1}{7} to have a denominator of 56 by multiplying numerator and denominator by 8: 1×87×8=856\frac{1 \times 8}{7 \times 8} = \frac{8}{56}.
Convert 18\frac{1}{8} to have a denominator of 56 by multiplying numerator and denominator by 7: 1×78×7=756\frac{1 \times 7}{8 \times 7} = \frac{7}{56}.
Step 3: Add these equivalent fractions: 856+756=8+756=1556\frac{8}{56} + \frac{7}{56} = \frac{8 + 7}{56} = \frac{15}{56}.
Step 4: The fraction 1556\frac{15}{56} is already in its simplest form.
Therefore, the solution to the problem is 1556 \frac{15}{56} .

3

Final Answer

1556 \frac{15}{56}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Find common denominator before adding fractions together
  • Technique: Multiply 17 \frac{1}{7} by 8 to get 856 \frac{8}{56}
  • Check: Verify 856+756=1556 \frac{8}{56} + \frac{7}{56} = \frac{15}{56}

Common Mistakes

Avoid these frequent errors
  • Adding denominators together instead of finding common denominator
    Don't add 7 + 8 = 15 to get 215 \frac{2}{15} ! This completely changes the fraction values and gives a wrong answer. Always find the common denominator first by multiplying the different denominators.

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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Because fractions represent parts of a whole, and you can only add parts that are the same size! Adding 17+18 \frac{1}{7} + \frac{1}{8} is like adding 1 slice of a 7-piece pizza to 1 slice of an 8-piece pizza - they're different sizes!

Is 56 always the common denominator for 7 and 8?

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Yes! Since 7 and 8 share no common factors (they're relatively prime), their Least Common Multiple is always 7×8=56 7 \times 8 = 56 .

Do I need to simplify 1556 \frac{15}{56} ?

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Check if 15 and 56 have common factors! Since 15 = 3 × 5 and 56 = 8 × 7, they share no common factors, so 1556 \frac{15}{56} is already simplified.

What if the denominators were larger numbers?

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The process stays the same! Find the LCM of the denominators, convert each fraction, then add. You might want to use prime factorization for larger numbers to find the LCM more easily.

Can I use cross-multiplication for this problem?

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No, cross-multiplication only works for equations with one fraction on each side. For adding fractions, you must use the common denominator method.

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