Solve the Fraction Equation: Isolating X in (2-x)/(5*(3+x)-15) = 2/7

Fractional Equations with Cross-Multiplication

Solve for X:

2x5×(3+x)15=27 \frac{2-x}{5\times(3+x)-15}=\frac{2}{7}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Find X
00:03 Make sure to open parentheses properly, multiply by each factor
00:16 Group terms
00:28 Multiply by denominators to eliminate fractions
00:42 Make sure to open parentheses properly, multiply by each factor
00:52 Arrange the equation so that one side has only the unknown X
00:59 Group terms
01:02 Isolate X
01:07 And this is the solution to the problem

Step-by-step written solution

Follow each step carefully to understand the complete solution
1

Understand the problem

Solve for X:

2x5×(3+x)15=27 \frac{2-x}{5\times(3+x)-15}=\frac{2}{7}

2

Step-by-step solution

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

  • Step 1: Cross-multiply to eliminate the fraction.
  • Step 2: Simplify both sides of the equation.
  • Step 3: Solve for x x .

Now, let's work through each step:

Step 1: Begin by cross-multiplying:

(2x)×7=2×(5×(3+x)15) (2-x) \times 7 = 2 \times (5 \times (3+x) - 15)

This simplifies to:

7(2x)=2(5(3+x)15) 7(2-x) = 2(5(3+x) - 15)

Step 2: Simplify both sides of the equation.
First, simplify the right-hand side:

5(3+x)=15+5x 5(3+x) = 15 + 5x

Then:

5(3+x)15=15+5x15=5x 5(3+x) - 15 = 15 + 5x - 15 = 5x

So, the equation becomes:

7(2x)=2(5x) 7(2-x) = 2(5x)

Distribute and simplify both sides:

Left-hand side: 147x 14 - 7x

Right-hand side: 10x 10x

Thus, the equation is now:

147x=10x 14 - 7x = 10x

Step 3: Solve for x x .
Rearrange to isolate x x :

14=10x+7x 14 = 10x + 7x

14=17x 14 = 17x

Divide both sides by 17 to solve for x x :

x=1417 x = \frac{14}{17}

Therefore, the solution to the problem is x=1417 x = \frac{14}{17} .

3

Final Answer

1417 \frac{14}{17}

Key Points to Remember

Essential concepts to master this topic
  • Cross-Multiplication: When one fraction equals another, multiply diagonally to eliminate fractions
  • Simplify First: Calculate 5(3+x)15=5x 5(3+x) - 15 = 5x before cross-multiplying
  • Verify Answer: Substitute x=1417 x = \frac{14}{17} back into original equation ✓

Common Mistakes

Avoid these frequent errors
  • Forgetting to simplify the denominator before cross-multiplying
    Don't cross-multiply 2x5(3+x)15=27 \frac{2-x}{5(3+x)-15} = \frac{2}{7} directly without simplifying = complicated algebra with wrong setup! Students get lost in messy calculations. Always simplify 5(3+x)15=5x 5(3+x) - 15 = 5x first to make cross-multiplication manageable.

Practice Quiz

Test your knowledge with interactive questions

Solve for X:

\( x - 3 + 5 = 8 - 2 \)

FAQ

Everything you need to know about this question

Why do we cross-multiply instead of finding a common denominator?

+

Cross-multiplication works perfectly when you have one fraction equals another fraction. It's faster than finding LCD because you multiply (2x)×7=2×5x (2-x) \times 7 = 2 \times 5x in one step!

How do I know if I simplified the denominator correctly?

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Distribute first: 5(3+x)=15+5x 5(3+x) = 15 + 5x , then subtract: 15+5x15=5x 15 + 5x - 15 = 5x . The 15 terms cancel out completely, leaving just 5x 5x .

What if I get a negative answer?

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Negative answers are completely valid! Always double-check by substituting back. In this problem, we got a positive fraction 1417 \frac{14}{17} , but negatives happen too.

Can I solve this without cross-multiplying?

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Yes! You could multiply both sides by 7×5x=35x 7 \times 5x = 35x to clear fractions, but cross-multiplication is much simpler for this equation type.

How do I check if my final answer is correct?

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Substitute x=1417 x = \frac{14}{17} into the original equation. Calculate both sides separately: left side should equal right side. If 27=27 \frac{2}{7} = \frac{2}{7} , you're correct!

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