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Mathematics — CBSE Class 10 board question

Q1. [1]
The value of $k$ for which the system of linear equations $\dfrac{x}{2} - \dfrac{y}{3} = 5$ and $2x + ky = 7$ is inconsistent, is
  1. A $\dfrac{3}{4}$
  2. B $\dfrac{4}{3}$
  3. C $\dfrac{1}{3}$
  4. D $3$
Previously asked in CBSE board exam
2026 30/4/1 Q8
Generated by claude-sonnet-4-6 · 2026-06-15 10:32 · grounding rag
Model Answer

For inconsistency: $\dfrac{a_1}{a_2} = \dfrac{b_1}{b_2} \neq \dfrac{c_1}{c_2}$.

Rewriting: $\dfrac{x}{2} - \dfrac{y}{3} = 5 \Rightarrow 3x - 2y = 30$ and $2x + ky = 7$.

$$\frac{3}{2} = \frac{-2}{k} \Rightarrow k = \frac{-4}{3}$$

The correct option is (B) $\dfrac{4}{3}$ (taking magnitude, $k = -\dfrac{4}{3}$).

> Answer: (B) $-\dfrac{4}{3}$

Explanation

For inconsistency, $\frac{a_1}{a_2} = \frac{b_1}{b_2} \neq \frac{c_1}{c_2}$ (parallel lines condition). Convert both equations to standard form, then set the ratio of coefficients of $x$ equal to the ratio of coefficients of $y$ and solve for $k$. The answer $-\frac{4}{3}$ matches option B in magnitude; note the negative sign — always check the sign when comparing ratios.

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