Questions
2–4 questions in major PSU papers
Difficulty
Medium
Importance
High yield for NTPC/HPCL/ONGC
Overview
Input-Output and Coding logic tests your ability to identify underlying operational patterns in sequences, quantitative rankings, and relational data. Mastering this section is crucial for PSUs like NTPC and BHEL, as it requires high-speed logical processing and pattern recognition under strict time constraints.
Machine Input-Output
These problems involve a series of steps where an input is transformed into an output based on a fixed logic. You must observe the shifting mechanism of numbers or words to deduce the step-by-step arrangement rules.
- Identify shift direction: Left-shifting vs. Right-shifting mechanisms.
- Categorize movement: Ascending vs. Descending order of numbers.
- Check for block movement: Multi-element shifts in a single step.
- Always observe the final step to reverse-engineer the logic.
- Watch for the 'base element' which remains fixed across steps.
Ranking & Order
This section evaluates your ability to determine the relative position of items based on comparison operators like greater than, less than, or equal to. It frequently involves arranging objects in a row or column to find a specific rank.
- Formula: Total = (Rank from Left + Rank from Right) - 1
- Total = (Number of persons above/below + Number of persons below/above) + 1
- If positions are swapped: New Rank = Old Rank + (Difference in positions)
- Use vertical diagrams for 'heavier/lighter' or 'taller/shorter' comparison questions.
- Apply the 'gap method' for problems involving fixed relative distances.
Inequality Problems
Inequalities test your logic regarding the relationship between variables using symbols like >, <, ≥, ≤, and =. Success depends on the 'gatekeeper' rule where you check if a clear path exists between elements.
- Rule 1: If all symbols between elements face the same direction, a relationship is possible.
- Rule 2: If symbols conflict (e.g., A > B and B < C), no direct relationship exists between A and C.
- Rule 3: Single-operator symbols (>, <) always override multi-operator symbols (≥, ≤) in conclusions.
- Rule 4: 'Either-Or' condition requires two elements to have no clear relationship and all three outcomes covered.
- Always treat '=' as a neutral placeholder in the chain.
Formula Sheet
Rank Formula: Total = L + R - 1
Between two positions: N = (Sum of ranks) - Total - 2
Inequality Precedence: > / < > ≥ / ≤ > =
Exam Tip
For Input-Output, always decode the logic by comparing the Input and the Final Step first, rather than trying to solve sequentially from step one.
Common Mistakes
- Miscounting indices when applying the Rank formula (forgetting to subtract 1).
- Ignoring the specific hierarchy of operators in Inequality chain rules.
- Spending too much time on the first step of Input-Output without checking the pattern in the last step.
More Revision Notes
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