Let's break down the blood relation question step by step to determine the relationship between Devika's paternal grandfather and my sister.

Analyzing the Blood Relation Statement

The core statement is: "my sister's mother-in-law's only son is Devika's father."

Let's decode this part by part:

• My sister's mother-in-law: A person's mother-in-law is the mother of their spouse. So, this is the mother of my sister's husband.
• My sister's mother-in-law's only son: The mother of my sister's husband has only one son. Since she is the mother of my sister's husband, her only son must be my sister's husband.

So, we have deduced that "my sister's mother-in-law's only son" is actually my sister's husband.

Now, the statement continues: "... is Devika's father."

Combining our deduction: My sister's husband is Devika's father.

This means Devika is the daughter of my sister and my sister's husband.

Determining Devika's Paternal Grandfather's Relation

We need to find out how Devika's paternal grandfather is related to my sister.

• Devika's father: As established, Devika's father is my sister's husband.
• Devika's paternal grandfather: A paternal grandfather is the father of one's father. So, Devika's paternal grandfather is the father of Devika's father.

Since Devika's father is my sister's husband, Devika's paternal grandfather is the father of my sister's husband.

The father of a person's husband is that person's father-in-law.

Therefore, Devika's paternal grandfather is my sister's father-in-law.

Summary of Relations

Based on the analysis, Devika's paternal grandfather is the father of my sister's husband, which means he is my sister's father-in-law.

Revision Table: Key Blood Relations

Additional Information: Solving Blood Relation Puzzles

Blood relation questions often involve decoding a series of relationships. A good strategy is to break down the statement into smaller parts and identify the direct relationship between individuals mentioned. Start from the 'from' end of the relationship (e.g., "my sister's...") and move towards the 'to' end ("...only son"). Visual diagrams can also be helpful, though not strictly necessary for simpler problems like this one. Practice is key to mastering blood relation problems for competitive exams.