Solve: (-12¼) - (-8²/₇) Mixed Number Subtraction with Negatives

Mixed Number Subtraction with Double Negatives

(1214)(827)= (-12\frac{1}{4})-(-8\frac{2}{7})=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:04 Negative times negative is always positive, so we subtract
00:11 Multiply each fraction by the second denominator to find a common denominator
00:29 Convert to a larger mixed fraction
00:41 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

(1214)(827)= (-12\frac{1}{4})-(-8\frac{2}{7})=

2

Step-by-step solution

Let's solve the problem step-by-step:

  • Step 1: Convert mixed numbers to improper fractions.

For 1214-12\frac{1}{4}, convert to an improper fraction:

1214=(12+14)=(484+14)=494-12\frac{1}{4} = -\left(12 + \frac{1}{4}\right) = -\left(\frac{48}{4} + \frac{1}{4}\right) = -\frac{49}{4}

For 827-8\frac{2}{7}, convert to an improper fraction:

827=(8+27)=(567+27)=587-8\frac{2}{7} = -\left(8 + \frac{2}{7}\right) = -\left(\frac{56}{7} + \frac{2}{7}\right) = -\frac{58}{7}

  • Step 2: Subtract the second improper fraction from the first.

The operation becomes 494(587)-\frac{49}{4} - (-\frac{58}{7}), which simplifies to 494+587-\frac{49}{4} + \frac{58}{7}.

Find a common denominator for 494\frac{49}{4} and 587\frac{58}{7}. The least common denominator is 28.

Convert 494-\frac{49}{4} and 587\frac{58}{7} to equivalents with a denominator of 28:

494=49×74×7=34328-\frac{49}{4} = -\frac{49 \times 7}{4 \times 7} = -\frac{343}{28}

587=58×47×4=23228\frac{58}{7} = \frac{58 \times 4}{7 \times 4} = \frac{232}{28}

So, 494+587-\frac{49}{4} + \frac{58}{7} becomes:

34328+23228=343+23228=11128-\frac{343}{28} + \frac{232}{28} = \frac{-343 + 232}{28} = \frac{-111}{28}

  • Step 3: Simplify the improper fraction 11128\frac{-111}{28} to a mixed number form.

Divide 111-111 by 28, which gives 3-3 and a remainder of 27. Thus:

32728-3\frac{27}{28}

Therefore, the solution to the problem is 32728-3\frac{27}{28}.

3

Final Answer

32728 -3\frac{27}{28}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Subtracting a negative number means adding the positive
  • Technique: Convert 1214 -12\frac{1}{4} to 494 -\frac{49}{4} before operations
  • Check: Final answer 32728 -3\frac{27}{28} lies between -12¼ and -8²/₇ ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting that subtracting negative means adding positive
    Don't change (-12¼) - (-8²/₇) to (-12¼) + (-8²/₇) = -20+ mixed number! This ignores the double negative rule and makes the answer much too negative. Always remember: minus a negative equals plus a positive.

Practice Quiz

Test your knowledge with interactive questions

\( -5-(-2)= \)

-7-7-7-6-6-6-5-5-5-4-4-4-3-3-3-2-2-2-1-1-1000111222333444555666777

FAQ

Everything you need to know about this question

Why does subtracting a negative number become addition?

+

Think of it like this: removing a debt is the same as gaining money. When you subtract 827 -8\frac{2}{7} , you're removing something negative, which makes your result more positive!

How do I convert mixed numbers to improper fractions with negatives?

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For 1214 -12\frac{1}{4} , first convert the positive version: 1214=494 12\frac{1}{4} = \frac{49}{4} . Then apply the negative sign: 494 -\frac{49}{4} . Keep the negative with the whole fraction!

Why is the LCD 28 for denominators 4 and 7?

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LCD is the smallest number both denominators divide into. Since 4 and 7 share no common factors, multiply them: 4 × 7 = 28. This lets you add/subtract the fractions easily.

How do I know if my mixed number answer is in simplest form?

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Check if the fraction part can be reduced further. Since 27 and 28 share no common factors (27 = 3³, 28 = 4 × 7), 2728 \frac{27}{28} is already simplified!

What's the easiest way to check my work?

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Convert your answer back to the original format and see if it makes sense. 32728 -3\frac{27}{28} should be between 1214 -12\frac{1}{4} and 827 -8\frac{2}{7} since we're adding positive value to -12¼.

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