Pair of Linear Equations in Two Variables
RD Sharma
CBSE
Grade 10
Question:
Five years ago, Nuri was thrice as old as Sonu. Ten years later, Nuri will be twice as old as Sonu. How old are Nuri and Sonu?
Step-by-Step Solution
Key Concept: $N - 5 = 3(S - 5) \Rightarrow N - 3S = -10$. $N + 10 = 2(S + 10) \Rightarrow N - 2S = 10$. Subtracting gives $S = 20, N = 50$.
Equations: (1) $N - 3S = -10$, (2) $N - 2S = 10$. [1.0 Mark]
Subtract (1) from (2): $S = 20$. $N = 2(20) + 10 = 50$. Nuri is $50$ years and Sonu is $20$ years old. [1.0 Mark]
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🎯 Official CBSE Marking Scheme:
Forming linear equations: 1.0 Mark
Solving $N = 50, S = 20$: 1.0 Mark
Correct Answer:
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