Solve the Fraction Addition: 1/2 + 2/5 Step by Step

Fraction Addition with Unlike Denominators

Solve the following exercise:

12+25=? \frac{1}{2}+\frac{2}{5}=\text{?}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 Multiply each fraction by the second denominator to find a common denominator
00:12 Remember to multiply both numerator and denominator
00:23 Calculate the multiplications
00:31 Add under common denominator
00:37 Calculate the numerator
00:40 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:

12+25=? \frac{1}{2}+\frac{2}{5}=\text{?}

2

Step-by-step solution

To solve the problem of adding the fractions 12 \frac{1}{2} and 25 \frac{2}{5} , we will follow these steps:

  • Step 1: Determine a common denominator for the fractions.
  • Step 2: Convert each fraction to an equivalent fraction with this common denominator.
  • Step 3: Add the resulting fractions.

Now, let’s explore each step in detail:

Step 1: The denominators are 2 and 5. A common denominator can be found by multiplying these two numbers: 2×5=10 2 \times 5 = 10 . Therefore, 10 is our common denominator.

Step 2: Convert each fraction to have the common denominator of 10.
- For 12 \frac{1}{2} , multiply both the numerator and the denominator by 5:
12×55=510 \frac{1}{2} \times \frac{5}{5} = \frac{5}{10} .
- For 25 \frac{2}{5} , multiply both the numerator and the denominator by 2:
25×22=410 \frac{2}{5} \times \frac{2}{2} = \frac{4}{10} .

Step 3: Add the fractions 510\frac{5}{10} and 410\frac{4}{10}:
Combine the numerators while keeping the common denominator:
5+4=9 5 + 4 = 9 .
Thus, 510+410=910\frac{5}{10} + \frac{4}{10} = \frac{9}{10} .

Therefore, the sum of 12 \frac{1}{2} and 25 \frac{2}{5} is 910\frac{9}{10}.

3

Final Answer

910 \frac{9}{10}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Find common denominator before adding unlike fractions
  • Technique: Convert 12 \frac{1}{2} to 510 \frac{5}{10} and 25 \frac{2}{5} to 410 \frac{4}{10}
  • Check: Verify 510+410=910 \frac{5}{10} + \frac{4}{10} = \frac{9}{10} by adding numerators ✓

Common Mistakes

Avoid these frequent errors
  • Adding numerators and denominators separately
    Don't add 12+25 \frac{1}{2} + \frac{2}{5} as 37 \frac{3}{7} ! This gives a completely wrong answer because you can't add fractions with different denominators directly. 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 1+2 and 2+5 to get 3/7?

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Because fractions represent parts of different wholes! Adding 12 \frac{1}{2} (half of something) to 25 \frac{2}{5} (two-fifths of something) requires making the pieces the same size first.

How do I find the common denominator?

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Find the least common multiple (LCM) of the denominators. For 2 and 5, since they share no common factors, multiply them: 2×5=10 2 \times 5 = 10 .

Do I always multiply the denominators together?

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Not always! Only when the denominators have no common factors. For example, with 14+16 \frac{1}{4} + \frac{1}{6} , the LCM of 4 and 6 is 12, not 24.

What if my answer looks too big?

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Check if you can simplify your fraction! However, 910 \frac{9}{10} is already in lowest terms since 9 and 10 share no common factors.

How do I convert fractions to the same denominator?

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  • For 12 \frac{1}{2} : multiply by 55 \frac{5}{5} to get 510 \frac{5}{10}
  • For 25 \frac{2}{5} : multiply by 22 \frac{2}{2} to get 410 \frac{4}{10}

Can I use a different common denominator?

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Yes! You could use 20, 30, or any multiple of 10. But using the smallest common denominator keeps your numbers manageable and reduces calculation errors.

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