The average age of 5 family members is 25 years. Including the servant increases the average age by 40%. What is the servant's age?

Introduction / Context:
Average increase by a percentage upon adding one member suggests the new average equals old average times (1 + percentage). Use totals to get the added person’s age precisely.

Given Data / Assumptions:

• 5 members, mean 25 ⇒ total = 125.
• Including servant: 6 persons; mean increases by 40% ⇒ new mean = 25 * 1.4 = 35.

Concept / Approach:
New total = new mean * new headcount = 35 * 6. Servant's age = new total − old total.

Step-by-Step Solution:

Verification / Alternative check:
With servant 85, total becomes 210; average 210 / 6 = 35, which is exactly 40% above 25.

Why Other Options Are Wrong:
90, 73, 55: Do not produce a new average of 35 when recomputed.

Common Pitfalls:
Adding 40% of the total instead of 40% of the average, or applying the 40% to only one person's age erroneously.

Final Answer:
85 yr