Solve the Fraction Subtraction: 5/8 minus 3/10

Fraction Subtraction with Different Denominators

Solve the following exercise:

58310=? \frac{5}{8}-\frac{3}{10}=\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
00:07 We'll multiply by 5 and 4 respectively to find the common denominator
00:10 Make sure to multiply both numerator and denominator
00:18 Let's calculate the multiplications
00:26 Subtract with the common denominator
00:33 Let's calculate the numerator
00:38 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:

58310=? \frac{5}{8}-\frac{3}{10}=\text{?}

2

Step-by-step solution

To solve the subtraction problem 58310\frac{5}{8} - \frac{3}{10}, we first need to find a common denominator for the fractions.

  • Step 1: Determine the least common multiple (LCM) of the denominators 8 and 10.

To find the LCM of 8 and 10, list their multiples:

Multiples of 8: 8,16,24,32,40,8, 16, 24, 32, 40, \ldots
Multiples of 10: 10,20,30,40,50,10, 20, 30, 40, 50, \ldots

The smallest common multiple is 40. Therefore, the common denominator is 40.

  • Step 2: Adjust each fraction to the common denominator of 40.

Convert 58\frac{5}{8} to a fraction with a denominator of 40:

58=5×58×5=2540\frac{5}{8} = \frac{5 \times 5}{8 \times 5} = \frac{25}{40}

Convert 310\frac{3}{10} to a fraction with a denominator of 40:

310=3×410×4=1240\frac{3}{10} = \frac{3 \times 4}{10 \times 4} = \frac{12}{40}

  • Step 3: Subtract the fractions.

Subtract the numerators and place the result over the common denominator:

25401240=251240=1340\frac{25}{40} - \frac{12}{40} = \frac{25 - 12}{40} = \frac{13}{40}

The result is 1340\frac{13}{40}, which is already in its simplest form.

The solution to the problem is 1340\frac{13}{40}.

3

Final Answer

1340 \frac{13}{40}

Key Points to Remember

Essential concepts to master this topic
  • Common Denominator Rule: Find LCM of denominators before subtracting fractions
  • Conversion Technique: Transform 58 \frac{5}{8} to 2540 \frac{25}{40} by multiplying by 55 \frac{5}{5}
  • Verification Check: Confirm 25401240=1340 \frac{25}{40} - \frac{12}{40} = \frac{13}{40} cannot simplify further ✓

Common Mistakes

Avoid these frequent errors
  • Subtracting denominators along with numerators
    Don't subtract 5-3 = 2 and 8-10 = -2 to get 22 \frac{2}{-2} ! This treats fractions like separate numbers instead of parts of wholes. Always find a common denominator first, then subtract only the numerators.

Practice Quiz

Test your knowledge with interactive questions

Solve the following exercise:

\( \frac{8}{5}-\frac{4}{5}=\text{?} \)

FAQ

Everything you need to know about this question

Why can't I just subtract 5-3 and 8-10 directly?

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Fractions represent parts of different-sized wholes! 58 \frac{5}{8} means 5 pieces of something cut into 8 parts, while 310 \frac{3}{10} means 3 pieces cut into 10 parts. You need the same-sized pieces to subtract.

How do I find the LCM of 8 and 10 quickly?

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List multiples of the larger number first: 10, 20, 30, 40... Then check which one is also divisible by 8. Since 40 ÷ 8 = 5, the LCM is 40!

What if my answer comes out as an improper fraction?

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That's totally fine! 1340 \frac{13}{40} is a proper fraction, but if you got something like 4540 \frac{45}{40} , you could convert to mixed number or leave it as improper - both are correct!

Do I always need to simplify my final answer?

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Yes, always check if you can simplify! Look for common factors in the numerator and denominator. Since 13 and 40 share no common factors except 1, 1340 \frac{13}{40} is already in simplest form.

What if the denominators are really big numbers?

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Don't panic! The same steps work. You might use prime factorization to find the LCM more easily, or use the formula: LCM(a,b) = (a × b) ÷ GCD(a,b).

Can I use a calculator for this?

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For practice, try doing it by hand first to understand the concept. But yes, calculators can help verify your work - just make sure you understand why the steps work!

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