The average age of Sumit, Krishna, and Rishabh is 43 years. The average age of Sumit, Rishabh, and Rohit is 49 years. If Rohit is 54 years old, what is Krishna's present age (in years)?

Introduction:
This is an averages comparison problem with overlapping members. Two different 3-person averages are given, where two people (Sumit and Rishabh) are common to both groups. By converting averages into total sums, we can isolate the sum of the common members. Since Rohit's age is known, we can compute (Sumit + Rishabh) and then use it to find Krishna's age from the first group's total.

Given Data / Assumptions:

• Average(Sumit, Krishna, Rishabh) = 43
• Average(Sumit, Rishabh, Rohit) = 49
• Rohit = 54
• All ages are present ages in years

Concept / Approach:
Total for 3 persons = average * 3. Compute totals, remove Rohit to get common sum, then subtract from the first total to get Krishna.

Step-by-Step Solution:
Sumit + Krishna + Rishabh = 43 * 3 = 129Sumit + Rishabh + Rohit = 49 * 3 = 147Sumit + Rishabh = 147 - 54 = 93Krishna = 129 - 93 = 36

Verification / Alternative check:
Common sum 93 and Krishna 36 gives total 129 and average 43. Common sum 93 and Rohit 54 gives total 147 and average 49. Both match the question, so the result is correct.

Why Other Options Are Wrong:
48 years and 42 years: do not satisfy the first group average when combined with common sum 93.40 years: comes from using 49 - 43 as a direct difference without totals.34 years: would reduce the first group total below 129.

Common Pitfalls:
Subtracting averages instead of converting to sums.Forgetting to multiply by 3 for totals.Accidentally solving for Sumit or Rishabh instead of Krishna.

Final Answer:
36 years