Difficulty: Easy
Correct Answer: 10 years
Explanation:
Introduction / Context:This blends a past-time multiplicative relation with a present-time sum. Translate the past statement to an equation in present ages, then combine with the present sum to solve the system.
Given Data / Assumptions:
Concept / Approach:From the past relation express F in terms of S. Substitute into the present sum to compute S directly.
Step-by-Step Solution:
F − 4 = 5S − 20 ⇒ F = 5S − 16(5S − 16) + S = 44 ⇒ 6S = 60 ⇒ S = 10Verification / Alternative check:Then F = 34. Four years ago: F = 30, S = 6, and 30 = 5 * 6 ✓.
Why Other Options Are Wrong:6 and 8 are past values or misreads; 4 is inconsistent with the equations.
Common Pitfalls:Applying the “times” relationship to present ages instead of the correctly shifted past ages.
Final Answer:10 years
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