Averages with family ages: The average of father and mother is 35 years (sum = 70). The average of father, mother, and their only son is 27 years (sum = 81). Find the son’s present age.

Introduction / Context:
Averages convert directly to totals by multiplying by the number of persons. Comparing two totals here (parents vs. parents + son) yields the son’s age immediately.

Given Data / Assumptions:

• Average of father and mother = 35 ⇒ sum = 70.
• Average of father, mother, and son = 27 ⇒ sum = 81.

Concept / Approach:
The son’s age equals (sum of three) − (sum of the two). No algebra beyond totals is necessary.

Step-by-Step Solution:

Verification / Alternative check:

Why Other Options Are Wrong:

• 12, 10.5, 10 are not equal to the computed 11.

Common Pitfalls:

• Mistaking the average as (sum/number) and not converting properly back to totals.

Final Answer:
11 yr