Blood relations: Reasoning Ability Notes for Navy SSR

Blood Relations – Reasoning Ability (Navy SSR)

Goal:
Quickly recognise and deduce family relationships (parent, sibling, aunt/uncle, cousin, etc.) based on a set of statements.

1. Simple Explanation

Blood relations (or kinship relations) are the relationships that exist because two people share a biological ancestor.
They are usually grouped into two categories:

Direct line	Collateral line
Parent → Child → Grand‑parent → …	Sibling → Cousin → …
Grandchild, great‑grandchild, etc.	Aunt/Uncle, Niece/Nephew, etc.

Direct line = one person is an ancestor/descendant of the other.
Collateral line = two people share an ancestor but are not in a direct ancestor‑descendant chain.

2. Key Points & Rules

Relationship	Symbolic Notation	Definition	When it appears
Parent / Child	`P → C`	A is parent of B ⇔ B is child of A	Given directly
Sibling	`S1 ↔ S2`	Two persons share the same parent(s)	Same parent → siblings
Grandparent / Grandchild	`GP → GC`	GP is parent of a parent of the GC	Two generations up/down
Aunt / Uncle	`A ↔ P`	A is sibling of a parent of B	A ≠ B, shares ancestor at 2nd generation
Niece / Nephew	`N ↔ A`	N is child of A’s sibling	Inverse of Aunt/Uncle
Cousin	`C1 ↔ C2`	Two persons share a grandparent but not a parent	First cousin = share one set of grandparents
Second Cousin	`C1 ↔ C2`	Share a great‑grandparent but not a grandparent	Two generations removed
Great‑Aunt / Great‑Uncle	`GA ↔ GP`	Aunt/Uncle of a parent	One generation above aunt/uncle
Grand‑Niece / Grand‑NePhew	`GN ↔ GP`	Niece/NePhew of a grandparent	Two generations below

Important Rules

Transitivity:
If A → B and B → C, then A → C (grand‑parent, great‑grand‑parent, …).
Symmetry for collateral relations:
A is sibling of B ⇔ B is sibling of A.
A is aunt of B ⇔ B is niece of A.
Same‑generation:
Two people are considered cousins only if they share a common ancestor two generations up (grandparents) and do not share a parent.
Degree of cousinship:
- 1st cousin: share grandparents.
- 2nd cousin: share great‑grandparents only.
- 3rd cousin: share great‑great‑grandparents only, etc.
Removal:
If two people are in different generations, they are once removed, twice removed, etc.
Example: Your mother’s first cousin → your first cousin once removed.

3. Worked Example

Problem Statement

In a family, the following relationships are known:

A is the son of B.

C is the daughter of B.

D is the son of C.

E is the daughter of D.

Determine the relationship between A and E.

Step‑by‑Step Reasoning

Step	Relationship deduced	Explanation
1	`A` and `C` are siblings	Same parent `B`.
2	`D` is the child of `C` → `A` is the uncle of `D`	`A` is sibling of `D`’s parent.
3	`E` is the child of `D` → `A` is the grand‑uncle of `E`