Solve for X: Finding the Solution to (2/7)x - (2/3)x = 4

Fractional Coefficients with Common Denominators

Solve for X:

27x23x=4 \frac{2}{7}x-\frac{2}{3}x=4

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve
00:04 We want to isolate the unknown X
00:08 We'll multiply by the common denominator to eliminate fractions
00:30 Divide 21 by 7
00:35 Divide 21 by 3
00:46 Solve each multiplication separately
00:58 Collect terms
01:04 Isolate the unknown X
01:14 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 for X:

27x23x=4 \frac{2}{7}x-\frac{2}{3}x=4

2

Step-by-step solution

To solve the provided equation 27x23x=4 \frac{2}{7}x - \frac{2}{3}x = 4 , we need to combine like terms on the left-hand side. Let's work step-by-step:

  • Step 1: Identify the common denominator of the fractions 27 \frac{2}{7} and 23 \frac{2}{3} .
    The least common denominator of 7 and 3 is 21.

  • Step 2: Rewrite each term with the common denominator of 21:
    27x=2×37×3x=621x\frac{2}{7}x = \frac{2 \times 3}{7 \times 3}x = \frac{6}{21}x and
    23x=2×73×7x=1421x\frac{2}{3}x = \frac{2 \times 7}{3 \times 7}x = \frac{14}{21}x.

  • Step 3: Combine these like terms:
    621x1421x=61421x=821x\frac{6}{21}x - \frac{14}{21}x = \frac{6 - 14}{21}x = \frac{-8}{21}x.

  • Step 4: Rewrite the equation with the combined terms:
    821x=4\frac{-8}{21}x = 4.

  • Step 5: Solve for x x by multiplying both sides by the reciprocal of 821-\frac{8}{21}:
    x=4×218=4×218=848=10.5x = 4 \times \frac{21}{-8} = 4 \times -\frac{21}{8} = -\frac{84}{8} = -10.5 or 1012-10\frac{1}{2}.

Therefore, the solution to the equation is x=1012 x = -10\frac{1}{2} .

3

Final Answer

1012 - 10\frac{1}{2}

Key Points to Remember

Essential concepts to master this topic
  • Common Denominator: Find LCD to combine fractional terms efficiently
  • Technique: Convert 27x \frac{2}{7}x to 621x \frac{6}{21}x and 23x \frac{2}{3}x to 1421x \frac{14}{21}x
  • Check: Substitute x=1012 x = -10\frac{1}{2} : 27(10.5)23(10.5)=4 \frac{2}{7}(-10.5) - \frac{2}{3}(-10.5) = 4

Common Mistakes

Avoid these frequent errors
  • Subtracting fractions without common denominators
    Don't subtract 2723 \frac{2}{7} - \frac{2}{3} directly = wrong coefficient! This ignores that fractions need matching denominators to combine. Always find the LCD (21) first, then convert: 6211421=821 \frac{6}{21} - \frac{14}{21} = \frac{-8}{21} .

Practice Quiz

Test your knowledge with interactive questions

\( x+7=14 \)

\( x=\text{?} \)

FAQ

Everything you need to know about this question

Why can't I just subtract the numerators 2 - 2 = 0?

+

The denominators are different (7 and 3), so you can't directly subtract! Think of it like 2 apples - 2 oranges ≠ 0 fruit. You need the same "type" (denominator) first.

How do I find the LCD of 7 and 3?

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Since 7 and 3 are both prime numbers, their LCD is simply 7 × 3 = 21. If they shared common factors, you'd need to find the smallest number both divide into.

Why is my answer negative?

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When you combine the terms, you get 821x=4 \frac{-8}{21}x = 4 . Since the coefficient of x is negative, dividing 4 by a negative number gives a negative answer!

Can I convert to decimals instead?

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Yes! 270.286 \frac{2}{7} ≈ 0.286 and 230.667 \frac{2}{3} ≈ 0.667 , but working with exact fractions is more precise and avoids rounding errors.

How do I multiply by the reciprocal correctly?

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To solve 821x=4 \frac{-8}{21}x = 4 , multiply both sides by 218 \frac{21}{-8} . Remember: reciprocal flips the fraction and keeps the sign!

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