Add Mixed Numbers: Solving (-13¼) + (-9⅖) Step by Step

Mixed Number Addition with Negative Values

(1314)+(927)= (-13\frac{1}{4})+(-9\frac{2}{7})=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:06 Let's begin solving the problem.
00:09 We need to find the point on the axis.
00:13 Remember, a positive times a negative is always negative. So, we subtract.
00:19 To subtract, think of moving left on a number line.
00:27 Next, multiply each fraction by the other's denominator to find a common one.
00:48 Okay, let's calculate step by step.
00:53 And that's how we find the solution to our question!

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

(1314)+(927)= (-13\frac{1}{4})+(-9\frac{2}{7})=

2

Step-by-step solution

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

  • Step 1: Convert mixed numbers to improper fractions.
  • Step 2: Find the least common denominator.
  • Step 3: Perform the addition and convert back to a mixed number.

Let's work through each step:

Step 1: Convert mixed numbers to improper fractions.

1314 -13\frac{1}{4} = (13+14)=(524+14)=534 -\left( 13 + \frac{1}{4} \right) = -\left( \frac{52}{4} + \frac{1}{4} \right) = -\frac{53}{4}

927 -9\frac{2}{7} = (9+27)=(637+27)=657 -\left( 9 + \frac{2}{7} \right) = -\left( \frac{63}{7} + \frac{2}{7} \right) = -\frac{65}{7}

Step 2: Determine a common denominator. The least common multiple of 4 and 7 is 28.

Convert the fractions:

534=53×74×7=37128 -\frac{53}{4} = -\frac{53 \times 7}{4 \times 7} = -\frac{371}{28}

657=65×47×4=26028 -\frac{65}{7} = -\frac{65 \times 4}{7 \times 4} = -\frac{260}{28}

Step 3: Add the fractions:

37128+(26028)=371+26028=63128 -\frac{371}{28} + \left(-\frac{260}{28}\right) = -\frac{371 + 260}{28} = -\frac{631}{28}

Converting 63128 -\frac{631}{28} back to a mixed number:

Perform the division: 631÷2822 631 \div 28 \approx 22 remainder 15.

This gives us a mixed number: 221528 -22\frac{15}{28}

Therefore, the solution to the problem is 221528 -22\frac{15}{28} .

3

Final Answer

221528 -22\frac{15}{28}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Convert mixed numbers to improper fractions before adding
  • Technique: Find LCD: 4 and 7 have LCM of 28
  • Check: 63128=221528 -\frac{631}{28} = -22\frac{15}{28} when 631 ÷ 28 = 22 R 15 ✓

Common Mistakes

Avoid these frequent errors
  • Adding whole numbers and fractions separately
    Don't add -13 + (-9) = -22, then separately add 1/4 + 2/7! This ignores the different denominators and gives wrong results. Always convert to improper fractions first, then find a common denominator.

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 can't I just add the whole numbers and fractions separately?

+

Because the fractions have different denominators! You can't add 1/4 + 2/7 without converting to equivalent fractions with the same denominator first.

How do I convert a negative mixed number to an improper fraction?

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For 1314 -13\frac{1}{4} , multiply: 13 × 4 = 52, then add the numerator: 52 + 1 = 53. Keep the negative sign: 534 -\frac{53}{4} .

What's the easiest way to find the LCD of 4 and 7?

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Since 4 and 7 are both prime numbers with no common factors, their LCD is simply their product: 4 × 7 = 28.

How do I convert an improper fraction back to a mixed number?

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Divide the numerator by the denominator: 631÷28=22 631 ÷ 28 = 22 remainder 15 15 . So 63128=221528 -\frac{631}{28} = -22\frac{15}{28} .

Why is the final answer negative?

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Because we're adding two negative numbers! When you add negative values, the result is always more negative than either starting number.

Do I need to simplify 15/28?

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Check if 15 and 28 have common factors. Since 15 = 3 × 5 and 28 = 4 × 7, they share no common factors, so 1528 \frac{15}{28} is already simplified!

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