Rahul tells Anand, "Yesterday I defeated the only brother of the daughter of my grandmother." In this blood relation problem, whom did Rahul defeat?

Introduction / Context:
This puzzle describes Rahul defeating someone who is identified as the only brother of the daughter of his grandmother. We must determine exactly who this person is relative to Rahul. These problems test whether you can correctly interpret which daughter of the grandmother is being referred to and how that affects the identity of the only brother mentioned.

Given Data / Assumptions:
• Rahul has a grandmother.• That grandmother has at least one daughter.• Rahul refers to the daughter of his grandmother.• He then speaks of the only brother of that daughter.• Standard interpretation in such questions is that the grandmother is Rahul's paternal grandmother unless stated otherwise.• Rahul defeated this only brother.

Concept / Approach:
Consider Rahul's paternal grandmother. Her children include Rahul's father and possibly one or more daughters, such as a paternal aunt. The daughter of my grandmother in this context is naturally taken to be Rahul's paternal aunt. The only brother of this paternal aunt would be Rahul's father, assuming no other sons. Thus the person defeated by Rahul is his own father. This is the standard exam interpretation when the question is framed in this way.

Step-by-Step Solution:
Step 1: Let G be Rahul's grandmother.Step 2: The daughter of G is most naturally interpreted as Rahul's paternal aunt, although she could be another daughter in general.Step 3: The only brother of this daughter must be the only son of G.Step 4: In a typical interpretation, that son is Rahul's father.Step 5: Rahul says he defeated this only brother, which identifies the defeated person as his father.Step 6: Therefore, Rahul defeated his own father.

Verification / Alternative Check:
Imagine a family where the grandmother has two children: one son (Rahul's father) and one daughter (Rahul's aunt). The aunt is the daughter of Rahul's grandmother. Her only brother is then Rahul's father. Rahul defeating the only brother of the grandmother's daughter clearly means he defeated his father. This fits all parts of the description without ambiguity in the standard exam model.

Why Other Options Are Wrong:
His son: There is no mention of Rahul's son or any younger generation in the description.His brother: The person is described as the brother of his aunt, not Rahul's brother directly.His father in law: No marital relation is indicated; the chain goes entirely through Rahul's grandmother and her children.His uncle: The only brother is taken to be Rahul's father, not another sibling of the grandmother that would be an uncle.

Common Pitfalls:
Some candidates assume that the daughter of my grandmother must be Rahul's mother, which would make the only brother his maternal uncle. However in typical reasoning questions, my grandmother is understood as paternal grandmother unless further clarified. It is also important to note the phrase only brother, which suggests a unique son of that grandmother in the relevant branch.

Final Answer:
Rahul defeated his own father.