Solve Mixed Number Subtraction: 3⅓ - 2⅕ Step by Step

Mixed Number Subtraction with Improper Fractions

31321415= 3\frac{1}{3}-2\frac{14}{15}=

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:03 The formula for converting a mixed number to a fraction
00:15 We'll use this formula in our exercise and convert to fractions
00:44 Multiply to find the common denominator
01:04 Subtract with the common denominator
01:16 Reduce as much as possible
01:24 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

31321415= 3\frac{1}{3}-2\frac{14}{15}=

2

Step-by-step solution

To solve this problem, follow these steps:

  • Step 1: Convert each mixed number to an improper fraction.
  • Step 2: Find a common denominator for the fractions.
  • Step 3: Subtract the fractions.
  • Step 4: Simplify the result if needed.

Let's begin with Step 1:
Convert 3133\frac{1}{3} to an improper fraction:
313=3×3+13=1033\frac{1}{3} = \frac{3 \times 3 + 1}{3} = \frac{10}{3}
Convert 214152\frac{14}{15} to an improper fraction:
21415=2×15+1415=44152\frac{14}{15} = \frac{2 \times 15 + 14}{15} = \frac{44}{15}

Step 2: Find a common denominator for 103\frac{10}{3} and 4415\frac{44}{15}.
The least common multiple of 3 and 15 is 15, so we'll use 15 as the common denominator.

Step 3: Convert 103\frac{10}{3} to have the denominator of 15:
103=10×53×5=5015\frac{10}{3} = \frac{10 \times 5}{3 \times 5} = \frac{50}{15}

Now, perform the subtraction:
50154415=504415=615\frac{50}{15} - \frac{44}{15} = \frac{50 - 44}{15} = \frac{6}{15}

Step 4: Simplify 615\frac{6}{15}.
The greatest common divisor of 6 and 15 is 3, so divide the numerator and denominator by 3:
615=6÷315÷3=25\frac{6}{15} = \frac{6 \div 3}{15 \div 3} = \frac{2}{5}

Thus, the final answer is 25\frac{2}{5}.

3

Final Answer

25 \frac{2}{5}

Key Points to Remember

Essential concepts to master this topic
  • Convert: Change mixed numbers to improper fractions before subtracting
  • Common Denominator: Use LCM: 103=5015 \frac{10}{3} = \frac{50}{15} when LCM is 15
  • Verify: Check 25+21415=313 \frac{2}{5} + 2\frac{14}{15} = 3\frac{1}{3}

Common Mistakes

Avoid these frequent errors
  • Subtracting whole numbers and fractions separately
    Don't subtract 3-2=1 and then deal with fractions separately = wrong method! This ignores that 21415 2\frac{14}{15} is larger than 313 3\frac{1}{3} in the fractional part. Always convert to improper fractions first, then find common denominators.

Practice Quiz

Test your knowledge with interactive questions

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

FAQ

Everything you need to know about this question

Why can't I just subtract the whole numbers first?

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Because 1415 \frac{14}{15} is bigger than 13 \frac{1}{3} ! If you subtract whole numbers first, you'll need to borrow from the whole number, making it much more complicated. Converting to improper fractions avoids this confusion.

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

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Use the formula: improper fraction = (whole × denominator + numerator) / denominator. For 313 3\frac{1}{3} : 3×3+13=103 \frac{3 \times 3 + 1}{3} = \frac{10}{3}

What's the easiest way to find the common denominator?

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Look for the Least Common Multiple (LCM). Since 15 is already a multiple of 3, the LCM of 3 and 15 is just 15. When one denominator divides evenly into the other, use the larger one!

Do I always need to simplify my final answer?

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Yes, always simplify! 615 \frac{6}{15} and 25 \frac{2}{5} are equal, but 25 \frac{2}{5} is in lowest terms. Divide both numerator and denominator by their greatest common factor.

What if my answer is negative?

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That's possible when subtracting mixed numbers! If the second number is larger than the first, your answer will be negative. Just follow the same steps and include the negative sign in your final answer.

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