Pair of Linear Equations in Two Variables
RD Sharma
CBSE
Grade 10
Question:
If $3x + 4y = 12$ and $4x + 3y = 9$, then the value of $x - y$ is:
(a) $-3$
(b) $3$
(c) $-1$
(d) $1$
Step-by-Step Solution
Key Concept: Subtract 1st equation from 2nd: $(4x + 3y) - (3x + 4y) = 9 - 12 \Rightarrow x - y = -3$.
Subtract 1st equation from 2nd: $x - y = 9 - 12 = -3$. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Subtracting equations to get $x - y = -3$: 1.0 Mark
Correct Answer: $-3$
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