CBSE Class 8 Mathematics Linear Equations in Two Variables MCQs Set 31

Multiple Choice Questions (MCQs) for Class 8 Mathematics: Linear Equations in Two Variables

Explore reliable objective questions for Linear Equations in Two Variables tailored for Class 8 learners. Utilizing these Mathematics multiple-choice formats ensures thorough preparation and strengthens problem-solving speed for upcoming school assessments.

Practice Linear Equations in Two Variables MCQs for Class 8 Mathematics

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Multiple Choice Questions

Question 1: Given \( 5m-k=4 \) and \( 3m-5k=-24 \), the value of m is:
(a) \( 2 \)
(b) \( -2 \)
(c) \( \frac{14}{11} \)
(d) \( - \frac{2}{11} \)
Show Answer & Explanation

Answer: (a) \( 2 \)

Explanation:
1. Multiply the first equation by 5: 25m - 5k = 20. Subtract the second: 22m = 44.
2. So m = 2 (and k = 6).

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 2: Given \( 2x-5y=13 \) and \( 2x+y=-5 \), the value of x is:
(a) \( -1 \)
(b) \( -3 \)
(c) \( 1 \)
(d) \( 14 \)
Show Answer & Explanation

Answer: (a) \( -1 \)

Explanation:
1. Subtract the second equation from the first: -6y = 18, so y = -3.
2. Then 2x = -5 + 3 = -2, so x = -1.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 3: Given \( 4x-3y=6 \) and \( x-3y=-3 \), the value of y is:
(a) \( \frac{4}{3} \)
(b) \( -3 \)
(c) \( 2 \)
(d) \( -2 \)
Show Answer & Explanation

Answer: (c) \( 2 \)

Explanation:
1. Subtract the second equation from the first: 3x = 9, so x = 3.
2. Then 3y = x + 3 = 6, so y = 2.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 4: Given \( 2y=-6 \) and \( x-3y=13 \), the value of x is:
(a) \( \frac{13}{9} \)
(b) \( 19 \)
(c) \( 4 \)
(d) \( 22 \)
Show Answer & Explanation

Answer: (c) \( 4 \)

Explanation:
1. From 2y = -6, y = -3.
2. Then x = 13 + 3y = 13 - 9 = 4.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 5: Find x and y: \( x+2y+1=0 \) and \( 2x-3y-12=0 \).
(a) x = \( 5 \), y = \( 6 \)
(b) x = \( 5 \), y = \( 3 \)
(c) x = \( 4 \), y = \( 1 \)
(d) x = \( 3 \), y = \( -2 \)
Show Answer & Explanation

Answer: (d) x = \( 3 \), y = \( -2 \)

Explanation:
1. From the first equation x = -1 - 2y. Substituting: -2 - 4y - 3y = 12, so y = -2.
2. x = -1 + 4 = 3.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 6: The solution of \( x+y=7 \) and \( 5x+12y=7 \) is:
(a) x = \( 4 \), y = \( 3 \)
(b) x = \( 1 \), y = \( -1 \)
(c) x = \( 11 \), y = \( -4 \)
(d) x = \( 15 \), y = \( 5 \)
Show Answer & Explanation

Answer: (c) x = \( 11 \), y = \( -4 \)

Explanation:
1. From the first, x = 7 - y. Substituting: 35 - 5y + 12y = 7, so y = -4.
2. x = 7 + 4 = 11.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 7: The solution of \( 2x+3y=17 \) and \( 3x-2y=6 \) is:
(a) x = \( 11 \), y = \( -4 \)
(b) x = \( 4 \), y = \( 3 \)
(c) x = \( 15 \), y = \( 5 \)
(d) x = \( 1 \), y = \( -1 \)
Show Answer & Explanation

Answer: (b) x = \( 4 \), y = \( 3 \)

Explanation:
1. Multiply the first by 2 and the second by 3: 4x + 6y = 34 and 9x - 6y = 18.
2. Add: 13x = 52, so x = 4; then y = 3.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 8: The solution of \( 2x+y=35 \) and \( 3x+4y=65 \) is:
(a) x = \( 15 \), y = \( 5 \)
(b) x = \( 4 \), y = \( 3 \)
(c) x = \( 1 \), y = \( -1 \)
(d) x = \( 11 \), y = \( -4 \)
Show Answer & Explanation

Answer: (a) x = \( 15 \), y = \( 5 \)

Explanation:
1. Multiply the first by 4: 8x + 4y = 140. Subtract the second: 5x = 75, so x = 15.
2. Then y = 35 - 30 = 5.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 9: If y = 4, the value of x in \( 3x+4y=25 \) is:
(a) \( 8 \)
(b) \( 3 \)
(c) \( 4 \)
(d) \( 5 \)
Show Answer & Explanation

Answer: (b) \( 3 \)

Explanation:
1. Substitute y = 4: 3x + 16 = 25.
2. 3x = 9, so x = 3.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 10: For the equations of the form: \( 6x-5y=11 \) and \( 2x+y=17 \), the solution is:
(a) x = \( 5 \), y = \( 6 \)
(b) x = \( 8 \), y = \( 1 \)
(c) x = \( 7 \), y = \( 3 \)
(d) x = \( 6 \), y = \( 5 \)
Show Answer & Explanation

Answer: (d) x = \( 6 \), y = \( 5 \)

Explanation:
1. Multiply the second by 5: 10x + 5y = 85. Add to the first: 16x = 96, so x = 6.
2. Then y = 17 - 12 = 5.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 11: On eliminating y from \( 6x-5y=11 \) and \( 2x+y=17 \), the equation obtained in x is:
(a) \( 13x-95=0 \)
(b) \( 16x-96=0 \)
(c) \( 17x-85=0 \)
(d) \( 19x-91=0 \)
Show Answer & Explanation

Answer: (b) \( 16x-96=0 \)

Explanation:
1. Multiply the second equation by 5: 10x + 5y = 85.
2. Add it to 6x - 5y = 11: 16x = 96, i.e. 16x - 96 = 0.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 12: On eliminating y from \( 2x-y=10 \) and \( 3x+2y=22 \), the equation obtained in x is:
(a) \( 8x-48=0 \)
(b) \( 7x-42=0 \)
(c) \( 6x-48=0 \)
(d) \( 5x-30=0 \)
Show Answer & Explanation

Answer: (b) \( 7x-42=0 \)

Explanation:
1. Multiply the first by 2: 4x - 2y = 20. Add the second: 7x = 42.
2. So the equation is 7x - 42 = 0 (x = 6).

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 13: From \( \frac{x}{12-7}=\frac{y}{4-14}=\frac{1}{1-6} \), the values of x and y are:
(a) -1 and 4
(b) -1 and 2
(c) 4 and -2
(d) 2 and -1
Show Answer & Explanation

Answer: (b) -1 and 2

Explanation:
1. x/5 = 1/(-5) gives x = -1.
2. y/(-10) = 1/(-5) gives y = 2.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 14: Solving \( \frac{x}{a}+\frac{y}{b}=a+b \) and \( \frac{x}{a^2}+\frac{y}{b^2}=2 \) (a, b non-zero and a not equal to b), we get:
(a) \( x=a^2,\ y=b^2 \)
(b) \( x=a,\ y=2b \)
(c) \( x=a,\ y=b \)
(d) \( x=3a,\ y=b \)
Show Answer & Explanation

Answer: (a) \( x=a^2,\ y=b^2 \)

Explanation:
1. Put x = a² and y = b²: first equation gives a + b and the second gives 1 + 1 = 2, both satisfied.
2. The system has a unique solution, so x = a², y = b².

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 15: Solving \( \frac{2}{x}+\frac{3}{y}=13 \) and \( \frac{5}{x}-\frac{4}{y}=-2 \) (x, y non-zero):
(a) \( x=\frac{1}{4},\ y=\frac{1}{2} \)
(b) \( x=\frac{1}{3},\ y=\frac{1}{2} \)
(c) \( x=\frac{1}{2},\ y=\frac{1}{4} \)
(d) \( x=\frac{1}{2},\ y=\frac{1}{3} \)
Show Answer & Explanation

Answer: (d) \( x=\frac{1}{2},\ y=\frac{1}{3} \)

Explanation:
1. Put u = 1/x, v = 1/y: 2u + 3v = 13 and 5u - 4v = -2.
2. Multiply by 4 and 3 and add: 23u = 46, so u = 2, v = 3.
3. Hence x = 1/2 and y = 1/3.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 16: Solving \( \frac{6}{x+y}-\frac{3}{x-y}=2 \) and \( \frac{4}{x+y}+\frac{6}{x-y}=4 \):
(a) \( x=3,\ y=-\frac{1}{3} \)
(b) \( x=\frac{5}{2},\ y=-\frac{1}{2} \)
(c) \( x=\frac{5}{2},\ y=\frac{1}{2} \)
(d) \( x=\frac{4}{3},\ y=-\frac{2}{3} \)
Show Answer & Explanation

Answer: (b) \( x=\frac{5}{2},\ y=-\frac{1}{2} \)

Explanation:
1. Put u = 1/(x + y), v = 1/(x - y): 6u - 3v = 2 and 4u + 6v = 4.
2. Doubling the first and adding gives 16u = 8, so u = 1/2 and v = 1/3.
3. x + y = 2 and x - y = 3, so x = 5/2 and y = -1/2.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 17: Solving \( \frac{12}{x+y}+\frac{8}{x-y}=8 \) and \( \frac{27}{x+y}-\frac{12}{x-y}=3 \):
(a) \( x=\frac{5}{3},\ y=-\frac{1}{3} \)
(b) \( x=\frac{5}{2},\ y=\frac{1}{2} \)
(c) \( x=\frac{5}{4},\ y=\frac{1}{4} \)
(d) \( x=2,\ y=\frac{1}{3} \)
Show Answer & Explanation

Answer: (b) \( x=\frac{5}{2},\ y=\frac{1}{2} \)

Explanation:
1. Put u = 1/(x + y), v = 1/(x - y): 12u + 8v = 8 and 27u - 12v = 3.
2. Multiply by 3 and 2 and add: 90u = 30, so u = 1/3 and v = 1/2.
3. x + y = 3 and x - y = 2, so x = 5/2 and y = 1/2.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 18: Solving \( x+y=7xy \) and \( \frac{2}{x}+\frac{3}{y}=17 \) (x, y non-zero):
(a) \( x=\frac{1}{6},\ y=1 \)
(b) \( x=\frac{1}{4},\ y=\frac{1}{3} \)
(c) \( x=\frac{1}{3},\ y=\frac{1}{4} \)
(d) \( x=2,\ y=\frac{1}{5} \)
Show Answer & Explanation

Answer: (b) \( x=\frac{1}{4},\ y=\frac{1}{3} \)

Explanation:
1. Dividing x + y = 7xy by xy: 1/x + 1/y = 7.
2. With 2/x + 3/y = 17: subtract twice the first: 1/y = 3, so y = 1/3.
3. 1/x = 4, so x = 1/4.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 19: If \( x+y=5xy,\ y+z=7yz \) and \( z+x=6zx \) (x, y, z non-zero), then x, y, z are respectively:
(a) \( \frac{1}{2},\ \frac{1}{3},\ \frac{1}{4} \)
(b) \( \frac{1}{2},\ \frac{1}{3},\ \frac{1}{5} \)
(c) \( \frac{1}{2},\ \frac{1}{4},\ \frac{1}{3} \)
(d) \( \frac{1}{3},\ \frac{1}{4},\ \frac{1}{2} \)
Show Answer & Explanation

Answer: (a) \( \frac{1}{2},\ \frac{1}{3},\ \frac{1}{4} \)

Explanation:
1. Divide each equation by the product: 1/x + 1/y = 5, 1/y + 1/z = 7, 1/z + 1/x = 6.
2. Adding: 1/x + 1/y + 1/z = 9, so 1/z = 4, 1/x = 2 and 1/y = 3.
3. x = 1/2, y = 1/3, z = 1/4.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 20: The system \( 6x-2y=3 \) and \( kx-y=2 \) has a unique solution if:
(a) \( k\neq 3 \)
(b) \( k=-3 \)
(c) \( k=3 \)
(d) \( k=6 \)
Show Answer & Explanation

Answer: (a) \( k\neq 3 \)

Explanation:
1. Unique solution requires a₁/a₂ ≠ b₁/b₂, i.e. 6/k ≠ 2/1.
2. So k ≠ 3.

Teacher's Note:
1. Compare the ratios of the coefficients.
2. For k = 3 the lines are parallel.

Question 21: The system \( cx+3y+(3-c)=0 \) and \( 12x+cy-c=0 \) has infinitely many solutions when c equals:
(a) 6
(b) -6
(c) 12
(d) 3
Show Answer & Explanation

Answer: (a) 6

Explanation:
1. Infinitely many solutions need c/12 = 3/c = (3 - c)/(-c).
2. c/12 = 3/c gives c² = 36; 3/c = (3 - c)/(-c) gives -3 = 3 - c, so c = 6.
3. c = 6 satisfies all the ratios (c = -6 does not).

Teacher's Note:
1. All three ratios must be equal for coincident lines.
2. Check c = 6: 6/12 = 3/6 = -3/-6 = 1/2.

Question 22: For what value of k does the system \( (k-3)x+3y=k \), \( kx+ky=12 \) have infinitely many solutions?
(a) 6
(b) 9
(c) 12
(d) 3
Show Answer & Explanation

Answer: (a) 6

Explanation:
1. Coincident lines: (k - 3)/k = 3/k = k/12.
2. 3/k = k/12 gives k² = 36 and (k - 3)/k = 3/k gives k = 6.
3. So k = 6.

Teacher's Note:
1. The three ratios must be equal.
2. Check: 3/6 = 3/6 = 6/12.

Question 23: The pair of equations \( x-3y=3\text{ and }3x-9y=2 \) has:
(a) no solution
(b) exactly two solutions
(c) infinitely many solutions
(d) a unique solution
Show Answer & Explanation

Answer: (a) no solution

Explanation:
1. Compare a₁/a₂, b₁/b₂ and c₁/c₂.
2. 1/3 = -3/-9 = 1/3 but this differs from 3/2, so the lines are parallel and distinct.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Question 24: The pair of equations \( 2x+y=5\text{ and }4x+2y=10 \) has:
(a) no solution
(b) exactly two solutions
(c) infinitely many solutions
(d) a unique solution
Show Answer & Explanation

Answer: (c) infinitely many solutions

Explanation:
1. Compare a₁/a₂, b₁/b₂ and c₁/c₂.
2. 2/4 = 1/2 = 5/10, all ratios equal, so the lines coincide.

Teacher's Note:
1. Use elimination or substitution and check the answer in both equations.
2. A solution must satisfy both equations at the same time.

Multiple Choice Questions (MCQs) for Class 8 Mathematics Linear Equations in Two Variables

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