Difficulty: Easy
Correct Answer: 40 yr
Explanation:
Introduction / Context:This is a standard two-equation age problem. The current multiplicative relation (father is 4 times the son) is paired with an earlier-time multiplicative relation (7 times five years ago). Solving the simultaneous linear equations gives the exact ages.
Given Data / Assumptions:
Concept / Approach:Substitute F from the first relation into the second and solve for R, then compute F. This avoids introducing extra variables and minimizes algebraic errors.
Step-by-Step Solution:
F = 4RF − 5 = 7(R − 5)4R − 5 = 7R − 35 ⇒ 30 = 3R ⇒ R = 10F = 4R = 40Verification / Alternative check:Five years ago: father 35, Ravi 5; 35 is indeed 7 times 5. The data is fully consistent.
Why Other Options Are Wrong:84/70/35 are inconsistent with both relations; they fail either the current 4x relation or the 7x past relation.
Common Pitfalls:Reversing who is a multiple of whom, or applying the 5-year shift to only one person. Always subtract the same number of years from both ages when going backwards.
Final Answer:40 yr
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