Difficulty: Medium
Correct Answer: 10 years
Explanation:
Introduction / Context:We are given present and future age ratios. Represent the present ages using a single parameter and impose the future ratio after adding 5 years to both ages. Solve for the parameter to find A’s age.
Given Data / Assumptions:
Concept / Approach:Use cross-multiplication on the future ratio to get a linear equation in x. Compute A = 2x.
Step-by-Step Solution:
(2x + 5)/(3x + 5) = 3/4 ⇒ 4(2x + 5) = 3(3x + 5).8x + 20 = 9x + 15 ⇒ x = 5 ⇒ A = 2x = 10.Verification / Alternative check:
After 5 years: A = 15, B = 20 ⇒ 15 : 20 = 3 : 4 ✔.Why Other Options Are Wrong:
15 or 25 correspond to different x values that fail the future ratio; “Data inadequate” is false.Common Pitfalls:
Using 2x : 3x directly as 3 : 4 without adding 5 years to both.Final Answer:10 years
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