Solve: -1/2 + 3/4 - 1/5 - 4/5 Fraction Addition and Subtraction

Fraction Operations with Mixed Signs

12+34+15+(45)= -\frac{1}{2}+\frac{3}{4}+-\frac{1}{5}+(-\frac{4}{5})=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:10 Positive times negative always equals negative
00:24 Multiply by 2 to find common denominator
00:35 Add the fractions
00:55 Write the whole fraction as a whole number
01:00 Calculate the numerator
01:04 Positive times negative always equals negative
01:11 Convert from whole number to whole fraction with common denominator
01:20 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

12+34+15+(45)= -\frac{1}{2}+\frac{3}{4}+-\frac{1}{5}+(-\frac{4}{5})=

2

Step-by-step solution

To solve this problem, we must simplify the expression 12+34+(15)+(45) -\frac{1}{2} + \frac{3}{4} + (-\frac{1}{5}) + (-\frac{4}{5}) .

First, we need to find the least common denominator (LCD) for the fractions 2, 4, and 5. The LCD is 20.

Next, we convert each fraction to an equivalent fraction with the common denominator of 20:

  • 12-\frac{1}{2} becomes 1020-\frac{10}{20}
  • 34\frac{3}{4} becomes 1520\frac{15}{20}
  • 15-\frac{1}{5} becomes 420-\frac{4}{20}
  • 45-\frac{4}{5} becomes 1620-\frac{16}{20}

Now we perform the addition and subtraction:

1020+15204201620-\frac{10}{20} + \frac{15}{20} - \frac{4}{20} - \frac{16}{20}

Combine the numerators:

10+15416=15-10 + 15 - 4 - 16 = -15

Thus, the resulting fraction is:

1520-\frac{15}{20}

We simplify 1520-\frac{15}{20} by dividing both the numerator and the denominator by their greatest common divisor, which is 5:

1520=34-\frac{15}{20} = -\frac{3}{4}

Therefore, the solution to the problem is 34 -\frac{3}{4} , which corresponds to choice 2.

3

Final Answer

34 -\frac{3}{4}

Key Points to Remember

Essential concepts to master this topic
  • LCD Rule: Find least common denominator to add/subtract unlike fractions
  • Technique: Convert 12 -\frac{1}{2} to 1020 -\frac{10}{20} using LCD 20
  • Check: Combine signs correctly: -10 + 15 - 4 - 16 = -15 ✓

Common Mistakes

Avoid these frequent errors
  • Adding denominators instead of finding LCD
    Don't add 12+34 -\frac{1}{2} + \frac{3}{4} as 26 \frac{2}{6} = wrong answer! Adding denominators creates meaningless fractions. Always find the LCD first, then convert all fractions before adding numerators.

Practice Quiz

Test your knowledge with interactive questions

What will be the sign of the result of the next exercise?

\( (-2)\cdot(-4)= \)

FAQ

Everything you need to know about this question

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

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Fractions represent parts of wholes. You can only add parts when they're from the same-sized whole! 12 \frac{1}{2} and 14 \frac{1}{4} are different sized pieces, so find the LCD first.

How do I handle the negative signs correctly?

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Treat negative fractions like negative numbers. 15+(45) -\frac{1}{5} + (-\frac{4}{5}) becomes 1545 -\frac{1}{5} - \frac{4}{5} . Keep track of each sign when combining numerators!

What's the fastest way to find the LCD of 2, 4, and 5?

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List multiples of the largest denominator first: 4, 8, 12, 16, 20... Stop when you find one that's divisible by all other denominators. 20 ÷ 2 = 10, 20 ÷ 4 = 5, 20 ÷ 5 = 4 ✓

Should I always simplify my final answer?

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Yes! Always reduce fractions to lowest terms. 1520 -\frac{15}{20} simplifies to 34 -\frac{3}{4} by dividing both parts by their GCD of 5.

Can I group positive and negative fractions separately?

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Absolutely! Group 34 \frac{3}{4} (positive) and 121545 -\frac{1}{2} - \frac{1}{5} - \frac{4}{5} (negatives). This can make the arithmetic easier to track.

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