Solve: 3/2 - 3/8 - 1/4 | Fraction Subtraction Problem

Fraction Subtraction with Mixed Denominators

Solve the following exercise:

323814=? \frac{3}{2}-\frac{3}{8}-\frac{1}{4}=\text{?}

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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 smallest common denominator
00:06 Therefore, we'll multiply 4 and 2 respectively to find the common denominator
00:09 Remember to multiply both numerator and denominator
00:22 Let's calculate the multiplications
00:32 Subtract under the common denominator
00:39 Let's calculate the numerator
00:45 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:

323814=? \frac{3}{2}-\frac{3}{8}-\frac{1}{4}=\text{?}

2

Step-by-step solution

To solve the problem 323814 \frac{3}{2} - \frac{3}{8} - \frac{1}{4} , follow these steps:

  • Step 1: Find the Least Common Denominator (LCD): The denominators are 2, 8, and 4. The smallest number that all these can divide into is 8. So, the LCD is 8.
  • Step 2: Convert each fraction to have a denominator of 8:
    • 32\frac{3}{2} becomes 128\frac{12}{8} because 32×44=128\frac{3}{2} \times \frac{4}{4} = \frac{12}{8}.
    • 38\frac{3}{8} is already with a denominator of 8.
    • 14\frac{1}{4} becomes 28\frac{2}{8} because 14×22=28\frac{1}{4} \times \frac{2}{2} = \frac{2}{8}.
  • Step 3: Perform the Subtraction:
    • First subtract the fractions: 12838=98\frac{12}{8} - \frac{3}{8} = \frac{9}{8}.
    • Then, subtract 28\frac{2}{8} from the result: 9828=78\frac{9}{8} - \frac{2}{8} = \frac{7}{8}.
  • Step 4: Simplify the Result: The fraction 78\frac{7}{8} is already in its simplest form.

Therefore, the solution to the problem is 78\frac{7}{8}.

3

Final Answer

78 \frac{7}{8}

Key Points to Remember

Essential concepts to master this topic
  • LCD Rule: Find least common denominator before subtracting fractions
  • Technique: Convert 32 \frac{3}{2} to 128 \frac{12}{8} by multiplying by 44 \frac{4}{4}
  • Check: Verify 1283828=78 \frac{12}{8} - \frac{3}{8} - \frac{2}{8} = \frac{7}{8}

Common Mistakes

Avoid these frequent errors
  • Subtracting fractions without finding LCD first
    Don't subtract 3238 \frac{3}{2} - \frac{3}{8} directly = impossible to get correct answer! You can't subtract fractions with different denominators. Always find the LCD and convert all fractions to equivalent fractions with the same denominator first.

Practice Quiz

Test your knowledge with interactive questions

\( \frac{1}{3}+\frac{1}{4}= \)

FAQ

Everything you need to know about this question

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

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Fractions represent parts of a whole. You can only subtract when the parts are the same size (same denominator). Think of it like trying to subtract 3 apples from 2 oranges - you need the same units first!

How do I find the LCD when I have three different denominators?

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List the multiples of each denominator: 2 (2,4,6,8...), 8 (8,16,24...), 4 (4,8,12...). The smallest number that appears in all lists is your LCD. Here, it's 8!

What if my LCD seems too big? Can I use a smaller number?

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The LCD must be divisible by all denominators. Using a smaller number means some fractions can't be converted, making subtraction impossible. Always use the true LCD!

Do I need to reduce my final answer?

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Always check if your answer can be simplified! Look for common factors in the numerator and denominator. In this case, 78 \frac{7}{8} is already in lowest terms.

Can I work from left to right, subtracting one fraction at a time?

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Yes! Convert all fractions to the LCD first, then work left to right: 12838=98 \frac{12}{8} - \frac{3}{8} = \frac{9}{8} , then 9828=78 \frac{9}{8} - \frac{2}{8} = \frac{7}{8} .

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