How to Solve Coded Blood Relation Problems
Decode operator-based family relationship chains and build a family tree to find the correct answer, with worked examples and practice.
Expected Interview Answer
Coded blood relation problems replace family-relationship words with arithmetic operators (like +, −, ×, ÷) or generic codes, and the fastest reliable method is to translate each coded operator into its real relationship, then draw a family tree symbol by symbol from left to right, resolving the final relationship by tracing the path on the tree.
Start by writing down the given legend mapping each operator to a relationship — for instance '+' might mean 'father of,' '−' might mean 'mother of,' '×' might mean 'brother of,' and '÷' might mean 'sister of' — and note the gender each operator implies, since gender is what makes 'sibling' resolve into 'brother' or 'sister' in the final answer. Then process the coded expression strictly left to right, adding each new person as a node connected to the previous one by the decoded relationship, building a small genealogy diagram rather than trying to hold the chain in your head. Once the tree is drawn, trace the path from the first person to the last person mentioned in the question and read off the compound relationship (e.g., father’s father is grandfather, mother’s brother is maternal uncle), being careful to track gender at every node since the same structural path yields a different answer depending on whether the connecting relative is male or female. The most common failure is skipping the diagram and trying to reason symbolically, which reliably produces errors once three or more operators are chained.
- Drawing the tree eliminates the working-memory overload of long coded chains
- Explicit gender tracking prevents uncle/aunt and grandfather/grandmother mix-ups
- The same left-to-right method scales cleanly from 2-operator to 5-operator chains
AI Mentor Explanation
A cricket academy uses code letters instead of relationship words to describe how players are connected through their coaching lineage — one letter for 'trained by,' one for 'assisted,' one for 'mentored.' To figure out how a young player is connected to a legendary coach three links away, you decode each letter and draw a small lineage tree node by node, exactly as you would build a family tree from coded blood relation symbols. Skipping the diagram and trying to track three decoded links in your head is exactly how players misidentify who mentored whom, the same error test-takers make when they skip drawing the family tree.
Step-by-Step Explanation
Step 1
Build the operator legend
List what each coded symbol (+, −, ×, ÷, or letter codes) means, noting the gender each relationship implies.
Step 2
Process left to right
Decode the expression one operator at a time, adding each new person as a connected node.
Step 3
Draw the family tree
Sketch nodes and connecting relationships rather than holding the chain in memory, especially for 3+ operators.
Step 4
Trace and name the final relation
Follow the path from first to last person on the tree and name the compound relationship, double-checking gender at each node.
What Interviewer Expects
- Correct decoding of every coded operator before reasoning
- Disciplined left-to-right processing without skipping links
- Explicit gender tracking at each node of the tree
- Willingness to draw a diagram rather than reason purely symbolically
Common Mistakes
- Reasoning about long chains mentally instead of drawing a family tree
- Losing track of gender, confusing uncle with aunt or grandfather with grandmother
- Misapplying the legend by swapping two similar coded operators
- Reading the chain in the wrong direction (e.g., "A + B" meaning A is father of B, not B is father of A)
Best Answer (HR Friendly)
“My approach is to first write out exactly what each coded symbol means, including gender, from the legend given in the question. Then I process the coded expression strictly left to right and sketch a small family tree as I go, rather than trying to hold four or five decoded relationships in my head. Once the tree is built, I trace the path from the first person to the last and read off the compound relationship, being careful about gender at every step since that is usually what separates a correct answer from an almost-correct one.”
Follow-up Questions
- How would you handle a coded chain where the same symbol appears with two different meanings across sub-questions?
- What changes in your approach when the question asks for the relationship in the reverse direction?
- How do you determine gender when a coded operator is ambiguous, like “sibling of”?
- Can you describe how you would verify your family tree once fully drawn?
MCQ Practice
1. If 'A + B' means A is the father of B, and 'B × C' means B is the brother of C, what is A to C?
A is father of B, and B is brother of C, meaning B and C are siblings with the same father, so A is also the father of C.
2. If 'P − Q' means P is the mother of Q, and 'Q + R' means Q is the father of R, what is P to R?
P is mother of Q, and Q is father of R, so P is the paternal grandmother of R.
3. If 'X ÷ Y' means X is the sister of Y, and 'Y × Z' means Y is the brother of Z, how is X related to Z?
X and Y are siblings, and Y and Z are also siblings, so X is Z’s sister.
Flash Cards
Best method for a 3+ operator coded blood relation chain? — Decode each operator and draw a family tree node by node instead of reasoning mentally.
What must you track at every node besides the relationship? — Gender — it determines whether the final answer is uncle vs aunt, grandfather vs grandmother, etc.
What is the most common error in coded blood relation problems? — Skipping the diagram and losing track of a decoded link partway through a long chain.
What should you check first before decoding the expression? — The legend mapping each symbol to its relationship, since the same symbol can differ between questions.