What conclusion can be drawn about the solution of the following system of linear equations in two variables: 3x + 2y = 7 2x + 3y = 7
- (a)More than two solution
- (b)Infinite solutions
- (c)Unique solution
- (d)No solution
Answer
Why
Correct — C. Compare the coefficient ratios of 3x + 2y = 7 and 2x + 3y = 7 before solving anything.
a₁/a₂ = 3/2 and b₁/b₂ = 2/3
3/2 ≠ 2/3, so the two lines have different slopes
Lines with different slopes meet at exactly one point — a unique solution → option (c)
Solving confirms it:
subtract: x − y = 0
add: 5x + 5y = 14
so x = y = 7/5
Why the others are wrong
- (a)More than two solution — More than two solutions is not a case a pair of straight lines can produce. Two lines either cross once, never meet, or coincide and share every point — there is no three-solution or four-solution outcome.
- (b)Infinite solutions — Infinite solutions needs a₁/a₂ = b₁/b₂ = c₁/c₂, that is, one equation a plain multiple of the other. This pair fails at the first ratio, since 3/2 ≠ 2/3.
- (d)No solution — No solution means parallel lines, which needs a₁/a₂ = b₁/b₂ ≠ c₁/c₂. The slopes here are −3/2 and −2/3, so the lines cross instead of running parallel.
Concept
For a₁x + b₁y = c₁ and a₂x + b₂y = c₂, three ratios settle the whole question:
a₁/a₂ ≠ b₁/b₂ → the lines intersect once, a unique solution.
a₁/a₂ = b₁/b₂ ≠ c₁/c₂ → parallel lines, no solution.
a₁/a₂ = b₁/b₂ = c₁/c₂ → one and the same line, infinitely many solutions.
Test the first pair of ratios before anything else. If they differ you are already done, and the actual values of x and y are never needed to answer.
Swapping the coefficients while keeping the same right-hand side forces x = y whenever the two coefficients differ, which is a quick sanity check once you have named the case.
Key facts
- 3/2 ≠ 2/3, so 3x + 2y = 7 and 2x + 3y = 7 meet at exactly one point.
- The solution is x = y = 7/5, since 3(7/5) + 2(7/5) = 35/5 = 7.
- A pair of linear equations in two variables has one solution, none, or infinitely many — never a finite number greater than one.
Study next
Common traps
- Checking a₁/a₂ = b₁/b₂ and forgetting c₁/c₂, the ratio that separates parallel from coincident
- Reading the two equal right-hand sides (7 and 7) as a sign that the equations are equivalent
This naming question also comes with a letter buried in the coefficients to be pinned down.
Also asked 17 Sep 2024, 09:00, Quant Q.15, where kx − 15y + 7 = 0 and 7x − 21y − 19 = 0 have no solution for k = 5, and 26 Sep 2024, 09:00, Quant Q.6, where the keyed partner for 5x + 7y − 8 = 0 is the parallel line 5x + 7y − 16 = 0.
Related PYQs
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