Subtract Mixed Numbers: (+1/5) - (+3¾) Step-by-Step

Fraction Subtraction with Mixed Numbers

(+15)(+334)= (+\frac{1}{5})-(+3\frac{3}{4})=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:07 Let's solve this problem together.
00:12 Remember, negative times positive is always negative. So, let's subtract.
00:18 Multiply each fraction by the second denominator to find a common denominator.
00:29 Alright, let's calculate.
00:35 And there we have it! That's the solution to the question.

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

(+15)(+334)= (+\frac{1}{5})-(+3\frac{3}{4})=

2

Step-by-step solution

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

  • Convert the mixed number to an improper fraction.

  • Find a common denominator for the fractions.

  • Perform the subtraction.

Now, let's work through each step:

Step 1: Convert the Mixed Number
Convert 334 3\frac{3}{4} to an improper fraction:

334=3×4+34=12+34=154 3\frac{3}{4} = \frac{3 \times 4 + 3}{4} = \frac{12 + 3}{4} = \frac{15}{4} .

Step 2: Find a Common Denominator
Identify a common denominator for 15 \frac{1}{5} and 154 \frac{15}{4} . The least common denominator (LCD) of 5 and 4 is 20.

Convert 15 \frac{1}{5} and 154 \frac{15}{4} to have denominator 20:

15=1×45×4=420 \frac{1}{5} = \frac{1 \times 4}{5 \times 4} = \frac{4}{20} and 154=15×54×5=7520 \frac{15}{4} = \frac{15 \times 5}{4 \times 5} = \frac{75}{20} .

Step 3: Subtract the Fractions
Subtract the fractions:

4207520=47520=7120 \frac{4}{20} - \frac{75}{20} = \frac{4 - 75}{20} = \frac{-71}{20} .

The resulting fraction can be converted back to a mixed number:

7120=31120 \frac{-71}{20} = -3\frac{11}{20} .

Therefore, the solution to the problem is 31120 -3\frac{11}{20} .

3

Final Answer

31120 -3\frac{11}{20}

Key Points to Remember

Essential concepts to master this topic
  • Conversion: Change mixed numbers to improper fractions first
  • Common Denominator: LCD of 5 and 4 is 20: 15=420 \frac{1}{5} = \frac{4}{20}
  • Check: Convert final answer back to mixed number form ✓

Common Mistakes

Avoid these frequent errors
  • Subtracting denominators instead of finding common denominators
    Don't subtract 15154 \frac{1}{5} - \frac{15}{4} by doing 5-4=1 in denominators = completely wrong answer! This ignores fraction rules and gives meaningless results. Always find the LCD and convert both fractions to equivalent fractions with the same denominator first.

Practice Quiz

Test your knowledge with interactive questions

a is negative number.

b is negative number.

What is the sum of a+b?

FAQ

Everything you need to know about this question

Why do I need to convert the mixed number first?

+

Converting 334 3\frac{3}{4} to 154 \frac{15}{4} makes subtraction much easier! Mixed numbers are harder to work with directly, so improper fractions simplify the process.

How do I find the LCD of 5 and 4?

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List multiples: 5: 5, 10, 15, 20... and 4: 4, 8, 12, 16, 20... The first number that appears in both lists is 20, so LCD = 20.

Why is my answer negative?

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Because 15 \frac{1}{5} is much smaller than 334 3\frac{3}{4} ! When you subtract a larger number from a smaller number, you always get a negative result.

How do I convert back to a mixed number?

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Divide: 71÷20=3 -71 ÷ 20 = -3 remainder 11 11 . So 7120=31120 \frac{-71}{20} = -3\frac{11}{20} . The remainder becomes the numerator of the fraction part.

Can I work with the mixed number directly?

+

It's much more complicated! You'd need to borrow from the whole number part since 15<34 \frac{1}{5} < \frac{3}{4} . Converting to improper fractions first is the cleaner approach.

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