Machine Input-Output

Step-by-step word/number rearrangement following a hidden rule.

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Machine Input-Output

Overview

Machine Input-Output is a reasoning topic where you are given an initial arrangement of words and/or numbers, and shown how a hypothetical "machine" rearranges them step-by-step until reaching a final output. Your job is to decode the hidden rule governing each step, then apply it to answer questions about intermediate or final arrangements.

This topic typically carries 5 questions in IBPS PO Prelims, often appearing as a single set. It tests pattern recognition, systematic thinking, and the ability to track multiple elements through sequential changes. Once you crack the rule, all five questions become quick marks—but missing the pattern can cost you the entire set. Mastering this topic is high-reward because the questions are predictable once the logic is understood.

The key challenge is that the rule is never stated explicitly. You must infer it by comparing the input with each subsequent step, observing which element moves and where it lands.

Key Concepts

**The machine follows a consistent rule at every step.** Whatever operation happens in Step 1 repeats in the same logical manner in Step 2, Step 3, and so on.

**Elements are typically rearranged, not removed or added.** The same words and numbers from the input appear in the output—only their positions change.

**Common operations involve sorting:** arranging words alphabetically (A→Z or Z→A) or numbers in ascending/descending order, one element per step.

**Position matters:** Elements may be picked from the left end, right end, or based on a specific property (smallest number, first word alphabetically).

**Dual-end movement is common:** One word may move to the left while one number moves to the right in the same step, or vice versa.

**The final output is the stopping point:** When no further rearrangement is needed (fully sorted), the machine halts.

**Counting steps from input:** Input is Step 0. The first rearrangement is Step 1. Questions often ask about Step 3 or Step 4, so track carefully.

Formulas / Key Facts

1. **Alphabetical order for words:** Compare first letters; if same, compare second letters (e.g., "bat" comes before "box").

2. **Ascending order:** Smallest to largest (12, 25, 38, 47).

3. **Descending order:** Largest to smallest (47, 38, 25, 12).

4. **Left-end placement:** The selected element moves to position 1 (leftmost).

5. **Right-end placement:** The selected element moves to the last position.

6. **Alternating pattern:** Words may go to one end, numbers to the other—or odd-positioned and even-positioned elements may follow different rules.

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Q1 · Machine Input-Output · MEDIUM
A word and number arrangement machine when given an input line of words and numbers rearranges them following a particular rule in each step. The following is an illustration of input and rearrangement: Input: 45 basket 12 orange 78 chair 33 table Step I: 12 45 basket orange 78 chair 33 table Step II: 12 basket 45 orange 78 chair 33 table Step III: 12 basket 33 45 orange 78 chair table Step IV: 12 basket 33 chair 45 orange 78 table Step V: 12 basket 33 chair 45 orange table 78 Step V is the last step of the rearrangement. As per the rules followed in the above steps, find the appropriate step for the following input: Input: 56 apple 89 pencil 23 eraser 41 bottle Which step number is the following output? 23 apple 41 bottle 56 eraser 89 pencil
Q2 · Machine Input-Output · EASY
A word and number arrangement machine when given an input line of words and numbers rearranges them following a particular rule in each step. The following is an illustration of input and rearrangement: Input: 18 blue 52 green 37 red 64 white Step I: blue 18 52 green 37 red 64 white Step II: blue 18 green 52 37 red 64 white Step III: blue 18 green 37 52 red 64 white Step IV: blue 18 green 37 red 52 64 white Step V: blue 18 green 37 red 52 white 64 Step V is the last step of the rearrangement. As per the rules followed in the above steps, find the appropriate step for the following input: Input: 29 cat 71 dog 43 fish 85 bird What will be Step III?
Q3 · Machine Input-Output · MEDIUM
A word and number arrangement machine when given an input line of words and numbers rearranges them following a particular rule in each step. The following is an illustration of input and rearrangement: Input: 34 lamp 67 phone 21 table 58 chair Step I: 67 34 lamp phone 21 table 58 chair Step II: 67 58 34 lamp phone 21 table chair Step III: 67 58 34 21 lamp phone table chair Step IV: 67 58 34 21 phone lamp table chair Step V: 67 58 34 21 phone table lamp chair Step VI: 67 58 34 21 phone table lamp chair Which step is the last step of the above arrangement?
Q4 · Machine Input-Output · EASY

Notes generated on 22 Jun 2026

Machine Input-Output

Machine Input-Output

Overview

Key Concepts

Formulas / Key Facts

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