Input-Output and Age-Based Reasoning
Input-Output and Age-Based Reasoning
A machine input-output question shows a line of words or numbers rearranged step by step by a hidden rule. Find the rule from the first two steps, then run it to the step asked. Age-based reasoning gives birth years or comparisons of ages and asks who is oldest, or someone's age, which is ordering with numbers attached.
1. Method Box
| Type | Method |
|---|---|
| Number rearrangement | Check whether each step moves the largest or smallest remaining number to the next place on the left |
| Word rearrangement | Check alphabetical order, or word length, one word placed per step |
| Number of steps | Count until the arrangement stops changing; a step that changes nothing is not counted |
| Ages from birth years | Earlier year = older; age in year Y = Y − birth year (birthday passed) |
| Ages with comparisons and values | Order first, then fill values from the given ages or a regular gap |
In "one element per step" machines, an element already in its right place costs no step
Ages "in arithmetic progression" go up by the same number each time
✗ The number of steps equals the number of elements | ✓ Elements already in place need no step; count the actual changes
✗ Born later means older | ✓ Born later means younger
हिंदी नोट: इनपुट-आउटपुट प्रश्न में पहले दो चरणों से नियम पहचानिए, फिर उसी नियम को आगे चलाइए। जन्म वर्ष जितना पहले, व्यक्ति उतना बड़ा।
Exam Pointer: These patterns had no verified NTPC shift in our check (input-output and age-puzzle pages found were from banking, BHEL and police papers) and are tagged syllabus-based. They appear in harder NTPC CBT-2 shifts.
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Number rearrangement machine
[Pattern: syllabus-based, PYQ-style]
Input: 34 18 72 45 26 61. Step I: 72 34 18 45 26 61. Step II: 72 61 34 18 45 26. The machine continues by the same rule.
EXAM LEVEL
Q. What is the rule, and what is step III?
Each step moves the largest remaining number to the next place from the left; the others keep their order. Step III moves 45: 72 61 45 34 18 26.
Answer: Largest remaining number moves left; 72 61 45 34 18 26
EXAMATLAS LEVEL
Q. Which step is the last, and what does it show?
Step IV moves 26 ahead of 18: 72 61 45 34 26 18. The numbers are now in descending order, so step IV is the last.
Answer: Step IV: 72 61 45 34 26 18
Pattern 2: Word rearrangement machine
[Pattern: syllabus-based, PYQ-style]
Input: train ticket station journey platform coach. Step I: coach train ticket station journey platform. Step II: coach journey train ticket station platform. The machine continues by the same rule.
EXAM LEVEL
Q. What is the rule, and what is step III?
Each step moves the alphabetically first remaining word to the next place from the left. Step III moves platform: coach journey platform train ticket station.
Answer: Alphabetical, one word per step; coach journey platform train ticket station
EXAMATLAS LEVEL
Q. How many steps are needed to complete the arrangement, and what is the last step?
Step IV moves station: coach journey platform station train ticket. Step V moves ticket: coach journey platform station ticket train. Now all are in order.
Answer: 5 steps; coach journey platform station ticket train
Pattern 3: Birth years and ages
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. A was born in 1998. B was born 3 years after A, C 2 years before B, and D 4 years after C. Who is the oldest and who is the youngest?
A 1998, B 2001, C 1999, D 2003. Earliest is A, latest is D.
Answer: A oldest, D youngest
EXAMATLAS LEVEL
Q. Using the same birth years, what are their ages after their birthdays in 2026, and who is exactly 2 years older than B?
A 28, B 25, C 27, D 23. C (27) is 2 years older than B (25).
Answer: 28, 25, 27, 23; C
Pattern 4: Ordering with age values
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. P is older than Q but younger than R. S is younger than Q, and T is older than R. Who is the oldest?
T > R > P > Q > S.
Answer: T
EXAMATLAS LEVEL
Q. In the same order, S is 22 and R is 31, and the ages of S, Q, P and R go up by the same number of years each time. T is 3 years older than R. Find Q's and T's ages.
From S (22) to R (31) there are three equal gaps: 9/3 = 3 years. So Q = 25, P = 28, R = 31, and T = 34.
Answer: Q 25, T 34
60-Second Revision
- Find the machine rule from the first two steps.
- Count only steps that change the arrangement.
- Earlier birth year means older.
- Order the people first, then attach the ages.
Next Step: Reasoning done. Take a full ExamAtlas RRB NTPC 2026 reasoning mock; attempt calendar, clock and series questions first, as each has a fixed method.