Solve the Fraction Equation: 7/5 - 7/15 - 1/3

Fraction Subtraction with Multiple Denominators

Solve the following exercise:

7571513=? \frac{7}{5}-\frac{7}{15}-\frac{1}{3}=\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 least common denominator
00:06 Therefore we'll multiply by 3 and 5 respectively to find the common denominator
00:09 Remember to multiply both numerator and denominator
00:22 Let's calculate the multiplications
00:33 Subtract under the common denominator
00:39 Let's calculate the numerator
00:48 Reduce the fraction as much as possible
00:52 Remember to divide both numerator and denominator
00:55 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:

7571513=? \frac{7}{5}-\frac{7}{15}-\frac{1}{3}=\text{?}

2

Step-by-step solution

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

  • Step 1: Identify the least common multiple (LCM) for the denominators 5, 15, and 3.
  • Step 2: Convert each fraction to equivalent fractions with the common denominator.
  • Step 3: Perform subtraction on these equivalent fractions.

Let's work through each step:

Step 1: The denominators are 5, 15, and 3. The LCM of these numbers is 15, as it is the smallest number that all denominators divide evenly.

Step 2:

  • Convert 75\frac{7}{5} to an equivalent fraction with a denominator of 15: 75=7×35×3=2115\frac{7}{5} = \frac{7 \times 3}{5 \times 3} = \frac{21}{15}.
  • 715\frac{7}{15} already has the denominator 15.
  • Convert 13\frac{1}{3} to an equivalent fraction with a denominator of 15: 13=1×53×5=515\frac{1}{3} = \frac{1 \times 5}{3 \times 5} = \frac{5}{15}.

Step 3: Subtract the fractions:

2115715515=217515=915. \frac{21}{15} - \frac{7}{15} - \frac{5}{15} = \frac{21 - 7 - 5}{15} = \frac{9}{15}.

Simplify 915\frac{9}{15} by dividing both numerator and denominator by their greatest common divisor (GCD), which is 3:

9÷315÷3=35. \frac{9 \div 3}{15 \div 3} = \frac{3}{5}.

Therefore, the solution to the problem is 35 \frac{3}{5} .

3

Final Answer

35 \frac{3}{5}

Key Points to Remember

Essential concepts to master this topic
  • Common Denominator: Find LCM of all denominators before subtracting fractions
  • Convert: Change 75 \frac{7}{5} to 2115 \frac{21}{15} by multiplying by 3
  • Check: Verify 35 \frac{3}{5} by converting back: 9÷15 = 0.6 ✓

Common Mistakes

Avoid these frequent errors
  • Subtracting fractions without finding common denominator
    Don't subtract 75715 \frac{7}{5} - \frac{7}{15} by doing 7-7=0 and 5-15=-10 = 010 \frac{0}{-10} ! You can't subtract fractions with different denominators directly because they represent different-sized pieces. Always find the LCM first and convert all fractions to equivalent fractions with the same denominator.

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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Because fractions represent parts of a whole! 75 \frac{7}{5} means 7 pieces of size 1/5, while 715 \frac{7}{15} means 7 pieces of size 1/15. You can't subtract different-sized pieces directly - you need to make them the same size first.

How do I find the LCM of 5, 15, and 3?

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List the multiples of each: 5: (5, 10, 15, 20...), 15: (15, 30...), 3: (3, 6, 9, 12, 15...). The smallest number that appears in all lists is 15!

What if I get a fraction that can be simplified?

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Always simplify! Find the GCD of numerator and denominator. For 915 \frac{9}{15} , both 9 and 15 divide by 3, giving us 35 \frac{3}{5} in lowest terms.

Can I convert to decimals instead?

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You could, but it's often messier! 75=1.4 \frac{7}{5} = 1.4 , 7150.467 \frac{7}{15} ≈ 0.467 , 130.333 \frac{1}{3} ≈ 0.333 . Working with fractions keeps everything exact and avoids rounding errors.

How do I check my answer is correct?

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Convert your answer 35 \frac{3}{5} to the common denominator: 35=915 \frac{3}{5} = \frac{9}{15} . Then verify: 2115715515=915 \frac{21}{15} - \frac{7}{15} - \frac{5}{15} = \frac{9}{15}

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