The present ages of a father and his son are 41 years and 16 years, respectively. In how many years will the father be exactly twice as old as his son?

Introduction / Context:
Find the time t such that future ages satisfy a multiplicative relation. Build and solve a linear equation in t.

Given Data / Assumptions:

• Father now = 41, son now = 16
• Require: 41 + t = 2(16 + t)

Concept / Approach:
Set up the future-time equation and isolate t.

Step-by-Step Solution:

Verification / Alternative check:
After 9 years: father 50, son 25 ⇒ 50 = 2 × 25, holds.

Why Other Options Are Wrong:
10, 15, 19 do not satisfy the doubling condition when tested.

Common Pitfalls:
Applying 2× to present ages instead of future ages or forgetting to add t to both.

Final Answer:
9 years.