Blood Relations – Study Notes for IBPS Clerk (Reasoning Ability)
Why Blood Relations?
IBPS Reasoning tests the ability to trace family relationships quickly.
A solid grasp of blood relation basics – how to read a family tree, count steps, and apply the transitive property – is essential for cracking these questions under time pressure.
1. Core Concepts
| Term | Definition | Example |
|---|---|---|
| Parent | Immediate ancestor (father or mother). | If A is parent of B, then B is child of A. |
| Child | Immediate descendant. | If A is parent of B, then B is child of A. |
| Sibling | Share at least one common parent. | B and C are siblings if both are children of A. |
| Grandparent / Grandchild | Two‑step ancestor/descendant. | A → B → C → D: A is grandparent of C, D is grandchild of B. |
| Great‑Grand‑… | Every additional “great‑” adds one more step. | A → B → C → D → E: A is great‑grandparent of E. |
| Aunt / Uncle | Sibling of a parent. | A is sibling of B’s parent → A is B’s aunt/uncle. |
| Niece / Nephew | Child of a sibling. | A is sibling of B → C is child of B → C is A’s niece/nephew. |
| Cousin | Share a common ancestor but not a parent. | B and C share grandparents → first cousins. |
| Removed | Difference in generation. | B is first cousin of C (same generation). D is child of C → B and D are first cousins once removed. |
Blood relation = biological lineage only → marital ties (in‑laws, step‑relations) are excluded.
2. The Family Tree as a Graph
- Vertices: Individuals
- Edges: Parent–child links (directed upward or downward)
The distance between two nodes (persons) equals the number of edges in the shortest path connecting them.
Key Rule:
If the shortest path between X and Y has length k, then X and Y are k‑step relatives.
The direction (up/down) determines whether the relation is ancestor, descendant, or cousin.
3. Deriving Relationships – A Step‑by‑Step Algorithm
-
Identify the Common Ancestor (CA).
Traverse upward from both persons until a shared ancestor is found. -
Count Upward Steps (u) and Downward Steps (d).
u = edges from X to CA; d = edges from Y to CA. -
Determine the Relationship.
- If u = 0 → X is CA itself (ancestor case).
- If *d =