Solve Mixed Number Subtraction: 3 7/15 minus 2 1/5

Mixed Number Subtraction with Different Denominators

3715215= 3\frac{7}{15}-2\frac{1}{5}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 First, convert mixed fractions to fractions
00:50 Multiply to find the common denominator
01:05 Subtract with the common denominator
01:15 Now convert to mixed fraction
01:20 Break down 19 into 15 plus 4
01:28 Break down the fraction into whole number and remainder
01:36 Convert proper fraction to whole number and add to mixed fraction
01:42 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

3715215= 3\frac{7}{15}-2\frac{1}{5}=

2

Step-by-step solution

To solve this problem, we will subtract the mixed numbers 37153\frac{7}{15} and 2152\frac{1}{5} by considering their whole number parts and fractions separately.

Step 1: Subtract the Whole Numbers
The whole number part of the first mixed number is 3, and for the second mixed number, it is 2. Subtracting these gives:

32=1 3 - 2 = 1

Step 2: Subtract the Fractional Parts
The fractional part of the first number is 715\frac{7}{15}, and for the second, it is 15\frac{1}{5}. We need a common denominator to subtract these fractions. The least common denominator for 15 and 5 is 15. Convert 15\frac{1}{5} to a fraction with denominator 15:

15=1×35×3=315 \frac{1}{5} = \frac{1 \times 3}{5 \times 3} = \frac{3}{15}

Now, subtract the fractions:

715315=7315=415 \frac{7}{15} - \frac{3}{15} = \frac{7 - 3}{15} = \frac{4}{15}

Step 3: Combine the Whole Number and Fractional Parts
The whole number part is 1, and the fractional part is 415\frac{4}{15}. Combining these gives:

1415 1\frac{4}{15}

Thus, the result of the subtraction 37152153\frac{7}{15} - 2\frac{1}{5} is:

14151\frac{4}{15}

Therefore, the solution to the problem is 14151\frac{4}{15}.

3

Final Answer

1415 1\frac{4}{15}

Key Points to Remember

Essential concepts to master this topic
  • Rule: Find common denominator for fractions before subtracting
  • Technique: Convert 15 \frac{1}{5} to 315 \frac{3}{15} using LCD 15
  • Check: Verify 1415+215=3715 1\frac{4}{15} + 2\frac{1}{5} = 3\frac{7}{15}

Common Mistakes

Avoid these frequent errors
  • Subtracting fractions with different denominators directly
    Don't subtract 71515 \frac{7}{15} - \frac{1}{5} as 610 \frac{6}{10} ! This ignores that denominators must be equal before subtracting numerators. Always find the LCD first and convert both fractions.

Practice Quiz

Test your knowledge with interactive questions

\( 5:\frac{2}{5}= \)

FAQ

Everything you need to know about this question

Why can't I just subtract 7-1=6 and 15-5=10?

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You can only subtract numerators when denominators are exactly the same. 715 \frac{7}{15} and 15 \frac{1}{5} have different denominators, so you must convert to a common denominator first!

How do I find the LCD of 15 and 5?

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Since 5 goes into 15 evenly (15 ÷ 5 = 3), the LCD is 15. Always check if the larger denominator is already a multiple of the smaller one!

What if the whole number part becomes negative?

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If you need to borrow from the whole number (like in 218158 2\frac{1}{8} - 1\frac{5}{8} ), convert one whole to an improper fraction first, then subtract normally.

Can I convert both mixed numbers to improper fractions instead?

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Yes! Convert 3715=5215 3\frac{7}{15} = \frac{52}{15} and 215=3315 2\frac{1}{5} = \frac{33}{15} , then subtract: 52153315=1915=1415 \frac{52}{15} - \frac{33}{15} = \frac{19}{15} = 1\frac{4}{15}

How do I check my answer is correct?

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Add your answer back to the second number: 1415+215 1\frac{4}{15} + 2\frac{1}{5} should equal 3715 3\frac{7}{15} . If it does, you're right!

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