From 4× now to 2× in 10 years: Dr. Pandey is four times his son's age at present. After 10 years, he will be twice his son's age. What is the son's current age?

Introduction / Context:
Two time-separated multiplicative relations allow a linear solution. Express the father's present age in terms of the son's age and apply the 10-year condition.

Given Data / Assumptions:

• Let son's present age be S; Dr. Pandey's present age is 4S.
• After 10 years: 4S + 10 = 2(S + 10).

Concept / Approach:
Solve the single linear equation for S.

Step-by-Step Solution:
1) 4S + 10 = 2S + 20.2) 2S = 10 ⇒ S = 5.

Verification / Alternative check:
Now: father 20, son 5 (4×). In 10 years: father 30, son 15 (2×). Works perfectly.

Why Other Options Are Wrong:
They do not satisfy both multiplicative relations.

Common Pitfalls:
Forgetting to add 10 to both ages in the future condition.

Final Answer:
5 years