Adding Fractions with Different Denominators: 1/5 and 1/3

Fraction Addition with Unlike Denominators

Solve the following exercise:

15+13=? \frac{1}{5}+\frac{1}{3}=\text{?}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:05 Multiply each fraction by the second denominator to find a common denominator
00:15 Remember to multiply both numerator and denominator
00:32 Calculate the multiplications
00:40 Add under common denominator
00:45 Calculate the numerator
00:48 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

Solve the following exercise:

15+13=? \frac{1}{5}+\frac{1}{3}=\text{?}

2

Step-by-step solution

To solve the problem of adding the fractions 15 \frac{1}{5} and 13 \frac{1}{3} , we follow these steps:

  • Step 1: Find a common denominator for the fractions. Since the denominators are 55 and 33, the least common multiple is 1515.
  • Step 2: Convert each fraction to this common denominator:
    - For 15 \frac{1}{5} , multiply both numerator and denominator by 33 (the denominator of the other fraction), resulting in 315 \frac{3}{15} .
    - For 13 \frac{1}{3} , multiply both numerator and denominator by 55 (the denominator of the other fraction), resulting in 515 \frac{5}{15} .
  • Step 3: Add the fractions now that they have a common denominator:
    315+515=3+515=815\frac{3}{15} + \frac{5}{15} = \frac{3+5}{15} = \frac{8}{15}.

Therefore, when you add 15 \frac{1}{5} and 13 \frac{1}{3} , the solution is 815 \frac{8}{15} .

3

Final Answer

815 \frac{8}{15}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Find the least common multiple of denominators first
  • Technique: Convert 15 \frac{1}{5} to 315 \frac{3}{15} and 13 \frac{1}{3} to 515 \frac{5}{15}
  • Check: Verify 315+515=815 \frac{3}{15} + \frac{5}{15} = \frac{8}{15} by adding numerators ✓

Common Mistakes

Avoid these frequent errors
  • Adding denominators together
    Don't add 15+13 \frac{1}{5} + \frac{1}{3} as 28 \frac{2}{8} ! This completely ignores fraction rules and gives meaningless results. 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, and different denominators mean different-sized parts! You can only add fractions when they represent the same size pieces (same denominator).

How do I find the least common multiple of 5 and 3?

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Since 5 and 3 are both prime numbers, their LCM is simply 5 × 3 = 15. For other numbers, list multiples of each until you find the smallest one they share.

Do I always multiply by the other fraction's denominator?

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This shortcut works when denominators have no common factors (like 5 and 3). But for fractions like 14+16 \frac{1}{4} + \frac{1}{6} , the LCM is 12, not 24!

Can this fraction be simplified further?

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815 \frac{8}{15} is already in lowest terms because 8 and 15 share no common factors other than 1. Always check if your final answer can be simplified!

What if I get confused with the multiplication step?

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Remember: whatever you do to the denominator, do to the numerator too! For 15 \frac{1}{5} , multiply both 1 and 5 by 3 to get 315 \frac{3}{15} .

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