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Input-Output

Reasoning Ability · Mains Reasoning

Overview

An input-output machine rearranges words or numbers step by step by a fixed rule; you identify the rule and predict any step.

Key points

Common rules: arrange numbers ascending/descending one per step; words alphabetically one per step.
Some machines apply arithmetic to numbers at each step.
Elements already placed stay fixed; the rest shift.
The final step is when the arrangement is complete.
Count steps carefully.

Explanation

Track which element moves at each step.
Mixed inputs may alternate numbers and words.
Write each step on a new line.
The number of steps is often one less than the number of elements.

Step by step

Set up the frame (table, rows, steps).
Apply definite clues, then branch.
Verify every clue before answering.

Examples

Input 45 12 78 33; each step moves the smallest remaining number to the left end → step 1: 12 45 78 33; step 2: 12 33 45 78 (final).
Words "cat dog ant bee" sorted alphabetically one per step → final: ant bee cat dog.
A rule "add 5 to each number" applied to 3 8 → 8 13.

Traps and advanced points

Trap: Assuming all elements move each step.
Trap: Miscounting steps.
Trap: Applying the rule to fixed elements.

Quick revision

Find the moving element.
Fixed elements stay.
Count steps.

Practice MCQs

In input-output questions, elements already placed usually —
1. stay fixed
2. move back
3. disappear
4. double
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Answer: (a) stay fixed. Fixed after placement.
A common rule arranges numbers —
1. all at once
2. randomly
3. by colour
4. one per step in order
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Answer: (d) one per step in order. Stepwise.
Words are often arranged —
1. by length only
2. randomly
3. in reverse always
4. alphabetically one per step
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Answer: (d) alphabetically one per step. Alphabetical.
The final step is reached when —
1. step 3 always
2. numbers end
3. words end
4. the arrangement is complete
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Answer: (d) the arrangement is complete. Completion.
Input: 45 12 78 33. If the machine places the smallest number first in step 1, step 1 is —
1. 78 45 33 12
2. 12 45 78 33
3. 45 12 33 78
4. 12 33 45 78
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Answer: (b) 12 45 78 33. Move 12 to the front.
Some machines apply —
1. only colours
2. only spellings
3. arithmetic to numbers at each step
4. no rules
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Answer: (c) arithmetic to numbers at each step. Arithmetic machines.
Counting steps carefully matters because questions ask —
1. the font
2. the machine name
3. what appears at a particular step
4. the colour
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Answer: (c) what appears at a particular step. Step-specific.
For 5 unordered numbers arranged ascending one per step, the maximum steps needed is usually —
1. 6
2. 10
3. 4
4. 5
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Answer: (c) 4. n − 1 placements.
Identifying the rule is easiest by comparing —
1. only the input
2. random steps
3. input with step 1 and step 2
4. only the last step
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Answer: (c) input with step 1 and step 2. Early steps reveal the rule.
If a question asks for the "third element from the right in step 3", you must —
1. write step 3 fully
2. guess
3. use the input
4. use the last step
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Answer: (a) write step 3 fully. Write it out.