Solve Linear Equations With Rationals
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8th Grade Math › Solve Linear Equations With Rationals
Solve for $x$ (distribute and combine like terms): $0.6(x+5)-0.2x=4$.
$x=1.5$
$x=4.5$
$x=2.5$
$x=3.5$
Explanation
This question tests solving linear equations with fraction/decimal coefficients using distributive property and combining like terms. The process involves distributing a(bx+c)=abx+ac (e.g., 2/3(x-6)=2x/3-4), collecting like terms (2x+3x=5x, 1/2x+1/4x=3/4x using common denominator), isolating the variable (move x terms one side, constants other), and solving (divide both sides); clearing fractions by multiplying by LCD simplifies arithmetic (equation with 1/2 and 3/4: multiply by 4 converts to integers). For the equation 0.6(x+5)-0.2x=4, distribute to get 0.6x + 3 - 0.2x = 4, combine x terms to 0.4x + 3 = 4, subtract 3 to get 0.4x = 1, and divide by 0.4 to find x=2.5. The correct process yields x=2.5, which matches choice B. A common error is mishandling the subtraction of 0.2x, such as treating it as addition, or decimal division errors. Steps: (1) clear fractions if desired (multiply by LCD), (2) distribute (remove parentheses), (3) collect like terms (combine x's, combine constants), (4) isolate x (add/subtract to get x terms one side, constants other), (5) divide (coefficient of x), (6) simplify (reduce fraction if needed), (7) check (substitute back). Common errors: distributing only first term, adding fractions without common denominator (1/2+1/3≠2/5), sign errors moving terms, dividing wrong (x/4=2 → x=8 not 0.5).
A school club sells snack packs. The cost (in dollars) is modeled by the equation $0.5(x+6)+1.25=0.8x-0.25$. Solve for $x$.
$x=20$
$x=15$
$x=5$
$x=10$
Explanation
This question tests solving linear equations with fraction/decimal coefficients using distributive property and combining like terms. The process involves distributing a(bx+c)=abx+ac (e.g., 2/3(x-6)=2x/3-4), collecting like terms (2x+3x=5x, 1/2x+1/4x=3/4x using common denominator), isolating the variable (move x terms one side, constants other), and solving (divide both sides); clearing fractions by multiplying by LCD simplifies arithmetic (equation with 1/2 and 3/4: multiply by 4 converts to integers). For the equation 0.5(x+6) + 1.25 = 0.8x - 0.25, distribute to get 0.5x + 3 + 1.25 = 0.8x - 0.25, combine constants to 0.5x + 4.25 = 0.8x - 0.25, subtract 0.5x from both sides to get 4.25 = 0.3x - 0.25, add 0.25 to both sides to get 4.5 = 0.3x, and divide by 0.3 to find x=15. The correct process yields x=15, which matches choice C. A common error is mishandling decimals, such as subtracting 0.5 from 0.8 incorrectly as 0.2 instead of 0.3, or forgetting to add the constants properly. Steps: (1) clear fractions if desired (multiply by LCD), (2) distribute (remove parentheses), (3) collect like terms (combine x's, combine constants), (4) isolate x (add/subtract to get x terms one side, constants other), (5) divide (coefficient of x), (6) simplify (reduce fraction if needed), (7) check (substitute back). Common errors: distributing only first term, adding fractions without common denominator (1/2+1/3≠2/5), sign errors moving terms, dividing wrong (x/4=2 → x=8 not 0.5).
Solve for $x$ (distribute and then combine like terms): $$2.5(x-1.2)-0.5x=6.4$$
$x=\frac{57}{10}$
$x=\frac{37}{10}$
$x=\frac{47}{10}$
$x=\frac{27}{10}$
Explanation
This problem tests solving linear equations with fraction/decimal coefficients using distributive property and combining like terms. Process: distribute a(bx+c)=abx+ac (2/3(x-6)=2x/3-4), collect like terms (2x+3x=5x, 1/2x+1/4x=3/4x using common denominator), isolate variable (move x terms one side, constants other), solve (divide both sides). Clearing fractions by multiplying by LCD simplifies arithmetic (equation with 1/2 and 3/4: multiply by 4 converts to integers). For this specific equation, distribute 2.5 to (x-1.2) to get 2.5x - 3, then subtract 0.5x yielding 2.5x - 0.5x - 3 = 6.4; combine to 2x - 3 = 6.4, add 3 to get 2x = 9.4, then divide by 2 to find x = 4.7 or 47/10. The correct process yields the answer x = 47/10. A common error is miscalculating the distribution like 2.5*1.2 as 2.5 instead of 3, leading to wrong values like 37/10. Steps: (1) clear fractions if desired (multiply by LCD), (2) distribute (remove parentheses), (3) collect like terms (combine x's, combine constants), (4) isolate x (add/subtract to get x terms one side, constants other), (5) divide (coefficient of x), (6) simplify (reduce fraction if needed), (7) check (substitute back). Common errors: distributing only first term, adding fractions without common denominator (1/2+1/3≠2/5), sign errors moving terms, dividing wrong (x/4=2 → x=8 not 0.5).
Solve for $x$. Clear fractions if it helps: $$\frac{5}{6}x-\frac{1}{3}(x-9)=12$$
$x=18$
$x=27$
$x=9$
$x=15$
Explanation
This problem tests solving linear equations with fraction/decimal coefficients using distributive property and combining like terms. Process: distribute $a(bx+c)=abx+ac$ ($\frac{2}{3}(x-6)=\frac{2x}{3}-4$), collect like terms ($2x+3x=5x$, $\frac{1}{2}x+\frac{1}{4}x=\frac{3}{4}x$ using common denominator), isolate variable (move x terms one side, constants other), solve (divide both sides). Clearing fractions by multiplying by LCD simplifies arithmetic (equation with $\frac{1}{2}$ and $\frac{3}{4}$: multiply by 4 converts to integers). For this specific equation, distribute $-\frac{1}{3}$ to (x-9) to get $-(\frac{1}{3})x + 3$, then add ($\frac{5}{6}$)x yielding ($\frac{5}{6}x - \frac{1}{3}x + 3 = 12$); combine to ($\frac{1}{2}x + 3 = 12$), subtract 3 to get ($\frac{1}{2}x = 9$), then multiply by 2 to find x = 18. The correct process yields the answer x = 18. A common error is distributing with the wrong sign, like subtracting instead of adding 3, leading to wrong values like x = 9. Steps: (1) clear fractions if desired (multiply by LCD), (2) distribute (remove parentheses), (3) collect like terms (combine x's, combine constants), (4) isolate x (add/subtract to get x terms one side, constants other), (5) divide (coefficient of x), (6) simplify (reduce fraction if needed), (7) check (substitute back). Common errors: distributing only first term, adding fractions without common denominator ($\frac{1}{2}+\frac{1}{3}\neq\frac{2}{5}$), sign errors moving terms, dividing wrong ($\frac{x}{4}=2 \rightarrow x=8$ not 0.5).
Solve for $x$ (clear fractions if you want): $$\frac{1}{2}x + \frac{3}{4} = \frac{5}{8}x - \frac{1}{4}.$$
$x=8$
$x=4$
$x=6$
$x=2$
Explanation
This question tests solving linear equations with fraction coefficients using combining like terms. Process: collect like terms ($ \frac{1}{2} x - \frac{5}{8} x = -\frac{1}{8} x $), isolate variable (move x terms one side, constants other), solve (divide both sides). Clearing fractions by multiplying by LCD 8 simplifies arithmetic (equation with 1/2, 3/4, 5/8, 1/4: multiply by 8 converts to integers). For the equation ($ \frac{1}{2} x + \frac{3}{4} = \frac{5}{8} x - \frac{1}{4} $), subtract ($ \frac{1}{2} x $) to get ($ \frac{3}{4} = \frac{1}{8} x - \frac{1}{4} $), add ($ \frac{1}{4} $) to get ($ 1 = \frac{1}{8} x $), multiply by 8 to find ($ x = 8 $). The correct process and answer is $ x = 8 $, verified by substitution: left ($ \frac{1}{2}(8) + 0.75 = 4 + 0.75 = 4.75 $), right ($ \frac{5}{8}(8) - 0.25 = 5 - 0.25 = 4.75 $). A common error is incorrect fraction addition, like $ \frac{3}{4} + \frac{1}{4} $ as $ \frac{3}{8} $. Steps: (1) clear fractions (multiply by 8: $ 4x + 6 = 5x - 2 $), (2) collect like terms, (3) isolate x (subtract 4x: $ 6 = x - 2 $, add 2: $ x=8 $), (4) check. Common errors: adding fractions without common denominator, sign errors moving terms, dividing wrong.
Solve for $x$.
$$1.5(x-2)-0.75x=6$$
$x=8$
$x=12$
$x=14$
$x=10$
Explanation
This problem tests solving linear equations with decimal coefficients using the distributive property. Process: distribute $1.5(x-2) = 1.5x - 3$, combine like terms ($1.5x - 0.75x = 0.75x$), isolate variable, solve. For $1.5(x-2) - 0.75x = 6$: distribute to get $1.5x - 3 - 0.75x = 6$, combine x terms to get $0.75x - 3 = 6$, add 3 to both sides to get $0.75x = 9$, divide by 0.75 to get $x = 12$. The correct answer is $x=12$. Common errors include arithmetic mistakes with decimals or forgetting to distribute the negative sign.
A science club is mixing solutions. The equation for the amount of concentrate is
$$0.25(4x-8)+1.5=5.5$$
Solve for $x$.
$x=8$
$x=4$
$x=6$
$x=5$
Explanation
This problem tests solving linear equations with decimals in a real-world context about mixing solutions. Process: distribute 0.25(4x-8) = x - 2, combine constants, isolate variable, and solve. Starting with 0.25(4x-8) + 1.5 = 5.5, distribute to get x - 2 + 1.5 = 5.5. Simplify left side: x - 0.5 = 5.5. Add 0.5 to both sides: x = 6. Common errors include incorrect distribution (0.25 × 4x = x, not 0.25x) or decimal arithmetic mistakes. Steps: (1) distribute carefully with decimals, (2) combine constants, (3) isolate x, (4) check by substituting back: 0.25(4·6-8) + 1.5 = 0.25(16) + 1.5 = 4 + 1.5 = 5.5 ✓.
Solve for $x$. Be sure to use the distributive property and combine like terms:
$$\frac{3}{4}(x-8)+\frac{1}{2}x=10$$
$x=8$
$x=\frac{32}{5}$
$x=\frac{64}{5}$
$x=\frac{16}{5}$
Explanation
This problem tests solving linear equations with fraction coefficients using distributive property and combining like terms. Process: distribute a(bx+c)=abx+ac, collect like terms using common denominators, isolate variable by moving x terms to one side and constants to the other, then solve by dividing both sides. For this equation: distribute 3/4(x-8) = 3x/4 - 6, so the equation becomes 3x/4 - 6 + x/2 = 10. To combine x terms, find common denominator: 3x/4 + x/2 = 3x/4 + 2x/4 = 5x/4. The equation is now 5x/4 - 6 = 10, so 5x/4 = 16, giving x = 64/5. Common errors include distributing incorrectly (forgetting to multiply both terms) or adding fractions without finding common denominators.
Solve for $x$. (You will need to distribute and then collect like terms.)
$$\frac{1}{4}(2x-12)+\frac{3}{8}x=3$$
$x=7$
$x=\frac{12}{7}$
$x=\frac{24}{7}$
$x=\frac{48}{7}$
Explanation
This problem tests solving linear equations with multiple fractions requiring distribution and combining like terms. Process: distribute 1/4(2x-12) = x/2 - 3, combine all x terms and constants, then solve. Starting with 1/4(2x-12) + 3x/8 = 3, distribute to get x/2 - 3 + 3x/8 = 3. To combine x terms, find LCD of 2 and 8, which is 8: 4x/8 + 3x/8 = 7x/8. The equation becomes 7x/8 - 3 = 3. Add 3 to both sides: 7x/8 = 6. Multiply by 8/7: x = 48/7. Common errors include incorrect distribution of fractions or adding fractions without common denominators. Steps: distribute carefully, find LCD for combining terms, isolate variable, and simplify final answer.
Solve for $x$. Multiply by an LCD to eliminate fractions: $$\frac{5}{6}x - \frac{1}{3} = \frac{1}{2}x + 3$$
$x=8$
$x=10$
$x=\frac{10}{3}$
$x=12$
Explanation
This problem tests solving linear equations with fraction coefficients by clearing fractions using LCD. Process: multiply entire equation by LCD of 6 to eliminate fractions, then solve the resulting integer equation. To solve: $\frac{5}{6}x - \frac{1}{3} = \frac{1}{2}x + 3$ → multiply by 6: $5x - 2 = 3x + 18$ → $5x - 3x = 18 + 2$ → $2x = 20$ → $x = 10$. Let me verify: $\frac{5}{6}(10) - \frac{1}{3} = \frac{50}{6} - \frac{2}{6} = \frac{48}{6} = 8$, and $\frac{1}{2}(10) + 3 = 5 + 3 = 8$ ✓. The correct answer is x = 10. Steps: (1) identify LCD as 6, (2) multiply every term by 6, (3) simplify to get 5x - 2 = 3x + 18, (4) collect x terms on left, (5) collect constants on right, (6) divide by 2. Common errors: forgetting to multiply every term by LCD, arithmetic mistakes when clearing fractions.