Pair of Linear Equations in Two Variables Class 10: MCQ and case study questions
15 multiple-choice questions and 2 case-based questions on the current (rationalised) syllabus, in the style of the board paper's Sections A and E. Try each one first; the answer, a one-line reason and a worked solution open on a tap.
15 MCQs (1 mark each)
2 case studies (4 marks each)
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Multiple-choice questions
Choose one option. Section A of the board paper has 18 MCQs of 1 mark each, spread over all chapters.
Q1
·1 mark·Multiple choiceConsistency and number of solutions
How many solutions does the pair \(x + 2y = 5\), \(3x + 6y = 12\) have?
(a)Exactly one
(b)None
(c)Infinitely many
(d)Exactly two
Show answer
Answer: (b) None
Why: a₁/a₂ = b₁/b₂ = 1/3 but c₁/c₂ = 5/12, so the lines are parallel.
\(\dfrac{a_1}{a_2} = \dfrac13\), \(\dfrac{b_1}{b_2} = \dfrac26 = \dfrac13\), \(\dfrac{c_1}{c_2} = \dfrac{5}{12} \ne \dfrac13\). The lines are parallel, so there is no solution.
If \(x + y = 7\) and \(2x - 3y = -1\), then \(x - y\) equals
(a)\(1\)
(b)\(-1\)
(c)\(7\)
(d)\(4\)
Show answer
Answer: (a) \(1\)
Why: Substitute x = 7 − y: 14 − 5y = −1 gives y = 3, x = 4.
\(x = 7 - y \Rightarrow 2(7 - y) - 3y = -1 \Rightarrow 14 - 5y = -1 \Rightarrow y = 3\), \(x = 4\). So \(x - y = 1\).
Q7
·1 mark·Multiple choiceConsistency and number of solutions
The lines represented by \(3x - 4y = 8\) and \(9x - 12y = 24\) are
(a)intersecting at one point
(b)parallel
(c)coincident
(d)perpendicular
Show answer
Answer: (c) coincident
Why: All three ratios are equal: 3/9 = −4/−12 = 8/24 = 1/3.
\(\dfrac39 = \dfrac{-4}{-12} = \dfrac{8}{24} = \dfrac13\). The second equation is \(3\) times the first, so the lines coincide.
Q8
·1 mark·Multiple choiceConsistency and number of solutions
Which statement is true for the pair \(5x + 2y = 9\) and \(2x - y = 0\)?
(a)The lines are parallel, so the pair has no solution
(b)The lines cross once, so the pair has exactly one solution
(c)The lines coincide, so every point of one line is a solution
(d)The lines are parallel, yet the pair has one solution
Show answer
Answer: (b) The lines cross once, so the pair has exactly one solution
Why: 5/2 ≠ 2/(−1), so the lines intersect: one solution (1, 2).
\(\dfrac{a_1}{a_2} = \dfrac52\), \(\dfrac{b_1}{b_2} = -2\); these differ, so there is exactly one solution: \(y = 2x\), \(9x = 9\), \(x = 1\), \(y = 2\).
Q9
·1 mark·Multiple choiceSituational problems
The sum of two numbers is \(50\) and their difference is \(14\). The larger number is
(a)\(32\)
(b)\(36\)
(c)\(18\)
(d)\(25\)
Show answer
Answer: (a) \(32\)
Why: Add x + y = 50 and x − y = 14: 2x = 64.
\(x + y = 50\), \(x - y = 14\). Adding, \(2x = 64\), so \(x = 32\) (and \(y = 18\)).
Q10
·1 mark·Multiple choiceSituational problems
\(3\) pens and \(2\) notebooks cost ₹\(110\), while \(2\) pens and \(3\) notebooks cost ₹\(115\). The cost of one notebook is
(a)₹\(20\)
(b)₹\(30\)
(c)₹\(45\)
(d)₹\(25\)
Show answer
Answer: (d) ₹\(25\)
Why: Add: 5(p + n) = 225; subtract: n − p = 5.
\(3p + 2n = 110\), \(2p + 3n = 115\). Adding: \(p + n = 45\); subtracting: \(n - p = 5\). So \(n = 25\), \(p = 20\).
Q11
·1 mark·Multiple choiceConsistency and number of solutions
For which value of \(a\) do \(ax + 4y = 8\) and \(5x + 10y = 20\) have infinitely many solutions?
(a)\(2\)
(b)\(4\)
(c)\(\dfrac52\)
(d)\(10\)
Show answer
Answer: (a) \(2\)
Why: b₁/b₂ = c₁/c₂ = 2/5, so a/5 must also be 2/5.
\(\dfrac{4}{10} = \dfrac{8}{20} = \dfrac25\), so \(\dfrac{a}{5} = \dfrac25 \Rightarrow a = 2\).
Q12
·1 mark·Multiple choiceGraphical representation
The lines \(y = 2x\) and \(y = -x + 6\) meet at the point
(a)\((4, 2)\)
(b)\((2, 4)\)
(c)\((-2, -4)\)
(d)\((3, 6)\)
Show answer
Answer: (b) \((2, 4)\)
Why: 2x = −x + 6 gives x = 2, then y = 4.
\(2x = -x + 6 \Rightarrow 3x = 6 \Rightarrow x = 2\), \(y = 4\). The point is \((2, 4)\).
Q13
·1 mark·Multiple choiceGraphical representation
The lines \(x - y = 1\) and \(x + y = 5\) and the \(y\)-axis enclose a triangle. Its area (in square units) is
(a)\(6\)
(b)\(12\)
(c)\(9\)
(d)\(18\)
Show answer
Answer: (c) \(9\)
Why: Vertices (0, −1), (0, 5) and (3, 2): base 6 on the y-axis, height 3.
The lines meet at \((3, 2)\) and cut the \(y\)-axis at \((0, -1)\) and \((0, 5)\). Area \(= \dfrac12 \times 6 \times 3 = 9\).
Q14
·1 mark·Multiple choiceSituational problems
Riya is \(4\) years older than twice her brother's age, and the sum of their ages is \(25\) years. Riya's age is
(a)\(18\) years
(b)\(7\) years
(c)\(21\) years
(d)\(14\) years
Show answer
Answer: (a) \(18\) years
Why: r = 2b + 4 and r + b = 25 give 3b + 4 = 25.
\(r = 2b + 4\), \(r + b = 25 \Rightarrow 3b + 4 = 25 \Rightarrow b = 7\), so \(r = 18\).
Q15
·1 mark·Multiple choiceConsistency and number of solutions
The pair \(2x - 3y = 4\) and \(6x - 9y = c\) is inconsistent when
(a)\(c = 12\)
(b)\(c \ne 12\)
(c)\(c = 4\) only
(d)\(c\) is any real number
Show answer
Answer: (b) \(c \ne 12\)
Why: a₁/a₂ = b₁/b₂ = 1/3, so no solution exactly when 4/c ≠ 1/3.
\(\dfrac26 = \dfrac{-3}{-9} = \dfrac13\). The pair has no solution when \(\dfrac{4}{c} \ne \dfrac13\), i.e. \(c \ne 12\); at \(c = 12\) the lines coincide.
Case study questions
Section E of the board paper has three case-based questions of 4 marks: a real-life passage, then parts of 1, 1 and 2 marks, with a choice (OR) on the 2-mark part.
Case study 1: School canteen (4 marks)
On Monday a group of friends bought \(4\) samosas and \(3\) glasses of juice from the school canteen for ₹\(130\). On Tuesday another group bought \(2\) samosas and \(5\) glasses of juice for ₹\(170\). Let one samosa cost ₹\(x\) and one glass of juice cost ₹\(y\).
(i) Write the pair of linear equations that describes the two purchases. [1 mark]
Show answer
Answer: \(4x + 3y = 130\), \(2x + 5y = 170\)
\(4x + 3y = 130\) and \(2x + 5y = 170\). A1
(ii) Are the lines representing these equations intersecting, parallel or coincident? Give a reason. [1 mark]
Show answer
Answer: Intersecting
\(\dfrac{a_1}{a_2} = 2 \ne \dfrac{b_1}{b_2} = \dfrac35\), so the lines intersect (unique solution). A1
(iii) Find the cost of one samosa and of one glass of juice. [2 marks]
Show answer
Answer: Samosa ₹\(10\), juice ₹\(30\)
Double the second equation: \(4x + 10y = 340\); subtract the first: \(7y = 210\) M1, \(y = 30\), \(x = 10\). A1
OR How much would \(6\) samosas and \(2\) glasses of juice cost? [2 marks]
A residents' welfare association is fencing a rectangular park. The fence around it is \(84\) m long, and the length of the park is \(6\) m more than twice its width. Let the length be \(l\) m and the width be \(w\) m.
(i) Write a pair of linear equations in \(l\) and \(w\). [1 mark]
Show answer
Answer: \(l + w = 42\), \(l - 2w = 6\)
\(2(l + w) = 84\), i.e. \(l + w = 42\), and \(l = 2w + 6\), i.e. \(l - 2w = 6\). A1
(ii) Find the width of the park. [1 mark]
Show answer
Answer: \(12\) m
Substitute \(l = 2w + 6\): \(3w + 6 = 42 \Rightarrow w = 12\) m. A1
(iii) Find the length and the area of the park. [2 marks]
Show answer
Answer: \(30\) m; \(360\ \text{m}^2\)
\(l = 2(12) + 6 = 30\) m A1; area \(= 30 \times 12 = 360\ \text{m}^2\). A1
OR The association later adds \(4\) m to the length and removes \(2\) m from the width. Find the new area. [2 marks]
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Answer: \(340\ \text{m}^2\)
New length \(34\) m, new width \(10\) m M1; area \(= 340\ \text{m}^2\). A1
Next steps for Pair of Linear Equations in Two Variables
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