alleryA father is three times as old as his son. After five years, his age will be two and a half times that of his son. The present age of the son is:
A15 years
B12 years
C18 years
D20 years
Answer & Solution
Correct answer: A. 15 years
1. Let the son's present age be $y$ and father's age be $x$.
2. Given $x = 3y$.
3. In 5 years: $(x + 5) = 2.5(y + 5) \Rightarrow x + 5 = 2.5y + 12.5$.
4. Substitute $x = 3y$: $3y + 5 = 2.5y + 12.5 \Rightarrow 0.5y = 7.5 \Rightarrow y = 15$.
5. Therefore, the son's present age is 15 years.
_Source: NCERT Class 10 Mathematics, Ch3 'Pair of Linear Equations in Two Variables'_
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