Solve the System: Using Substitution in 3x - 2y and 4x + 3y Equations

System of Equations with Complex Fractions

Solve the following equations for x and y using the substitution method.

{3x2y8+xy2=144x+3y52x2y3=20 \begin{cases} \frac{3x-2y}{8}+\frac{x-y}{2}=14 \\ \frac{4x+3y}{5}-\frac{2x-2y}{3}=20 \end{cases}

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Step-by-step video solution

Watch the teacher solve the problem with clear explanations
00:00 Solve the system of equations
00:05 Multiply by 8 to eliminate fractions
00:16 Open parentheses properly, multiply by each term
00:26 Collect terms
00:37 Isolate X
00:47 This is the value of X, we'll substitute it in the second equation to find Y
00:57 Multiply by 15 to eliminate fractions
01:04 Open parentheses properly, multiply by each term
01:16 Collect terms
01:34 Substitute the X value we found to find Y
01:49 Multiply by 7 to eliminate the fraction
02:01 Open parentheses properly, multiply by each term
02:12 Isolate Y
02:25 This is the value of Y
02:33 Now let's substitute the Y value to find X
02:50 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 the following equations for x and y using the substitution method.

{3x2y8+xy2=144x+3y52x2y3=20 \begin{cases} \frac{3x-2y}{8}+\frac{x-y}{2}=14 \\ \frac{4x+3y}{5}-\frac{2x-2y}{3}=20 \end{cases}

2

Step-by-step solution

To solve the given system of equations using substitution, follow these steps:

First, we simplify the given equations. Let's start with the first equation:

3x2y8+xy2=14. \frac{3x-2y}{8} + \frac{x-y}{2} = 14.

Find a common denominator for fractions on the left side. The common denominator of 8 and 2 is 8:

3x2y8+4(xy)8=143x2y+4x4y8=14. \frac{3x-2y}{8} + \frac{4(x-y)}{8} = 14 \rightarrow \frac{3x-2y+4x-4y}{8} = 14.

Simplify inside the fraction:

7x6y8=147x6y=112.(multiply through by 8) \frac{7x-6y}{8} = 14 \rightarrow 7x - 6y = 112. \quad \text{(multiply through by 8)}

This is our simplified form for the first equation.

Now, simplify the second equation:

4x+3y52x2y3=20. \frac{4x+3y}{5} - \frac{2x-2y}{3} = 20.

Find a common denominator for the fractions, which is 15:

3(4x+3y)5(2x2y)15=20. \frac{3(4x + 3y) - 5(2x - 2y)}{15} = 20.

Distribute and simplify:

12x+9y10x+10y15=202x+19y15=20. \frac{12x + 9y - 10x + 10y}{15} = 20 \rightarrow \frac{2x + 19y}{15} = 20.

Multiply through by 15 to clear the fraction:

2x+19y=300. 2x + 19y = 300.

Now, we have two simplified equations:

{7x6y=1122x+19y=300. \begin{cases} 7x - 6y = 112 \\ 2x + 19y = 300 \end{cases}.

From the first equation, solve for xx:

7x=6y+112x=6y+1127. 7x = 6y + 112 \rightarrow x = \frac{6y + 112}{7}.

Substitute x=6y+1127x = \frac{6y + 112}{7} into the second equation:

2(6y+1127)+19y=300. 2\left(\frac{6y + 112}{7}\right) + 19y = 300.

Distribute:

12y+2247+19y=300. \frac{12y + 224}{7} + 19y = 300.

Clear the fraction by multiplying through by 7:

12y+224+133y=2100. 12y + 224 + 133y = 2100.

Combine like terms:

145y+224=2100. 145y + 224 = 2100.

Subtract 224 from both sides:

145y=1876y=187614512.93. 145y = 1876 \rightarrow y = \frac{1876}{145} \approx 12.93.

Now, substitute y12.93y \approx 12.93 back into x=6y+1127x = \frac{6y + 112}{7}:

x=6(12.93)+1127=77.58+1127=189.58727.08. x = \frac{6(12.93) + 112}{7} = \frac{77.58 + 112}{7} = \frac{189.58}{7} \approx 27.08.

Therefore, the solution to the system is:

x27.08,y12.93 x \approx 27.08, \, y \approx 12.93 .

This corresponds to choice 1:

x=27.08,y=12.93 x = 27.08, y = 12.93 .

3

Final Answer

x=27.08,y=12.93 x=27.08,y=12.93

Key Points to Remember

Essential concepts to master this topic
  • Simplification: Clear fractions by finding common denominators before substitution
  • Technique: From 7x - 6y = 112, solve x = 6y+1127 \frac{6y + 112}{7}
  • Check: Substitute x ≈ 27.08, y ≈ 12.93 back into original equations ✓

Common Mistakes

Avoid these frequent errors
  • Skipping fraction simplification step
    Don't substitute directly into complex fraction equations = messy calculations with errors! Working with 3x2y8+xy2=14 \frac{3x-2y}{8}+\frac{x-y}{2}=14 directly leads to calculation mistakes. Always simplify to standard form like 7x - 6y = 112 first.

Practice Quiz

Test your knowledge with interactive questions

Solve the following equations:

\( \begin{cases} 2x+y=9 \\ x=5 \end{cases} \)

FAQ

Everything you need to know about this question

Why do I need to simplify the fractions first?

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Complex fractions make substitution very messy! By clearing fractions first, you get clean equations like 7x6y=112 7x - 6y = 112 that are much easier to work with during substitution.

How do I find the common denominator for different fractions?

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For 3x2y8+xy2 \frac{3x-2y}{8}+\frac{x-y}{2} , the LCD of 8 and 2 is 8. Convert xy2 \frac{x-y}{2} to 4(xy)8 \frac{4(x-y)}{8} , then combine!

What if I get decimal answers instead of whole numbers?

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That's completely normal! Many systems have decimal solutions. Keep your calculations precise and round only at the very end to avoid accumulating errors.

How can I check if my decimal answers are correct?

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Substitute your values back into the original equations with fractions. If 3(27.08)2(12.93)8+27.0812.93214 \frac{3(27.08)-2(12.93)}{8}+\frac{27.08-12.93}{2} \approx 14 , you're correct!

Which variable should I solve for first in substitution?

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Choose the variable that gives you the simplest expression. From 7x - 6y = 112, solving for x gives x=6y+1127 x = \frac{6y + 112}{7} which is manageable.

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