Direction sense: Reasoning Ability Notes for Bihar PSC

Direction Sense – Reasoning Ability (Bihar PSC)

1. Simple Explanation

Direction sense tests your ability to keep track of relative positions of objects or people as they move in different directions.

Think of a clock face or a cardinal‑direction compass (N, NE, E, SE, S, SW, W, NW).
When a person moves “to the left” or “to the right”, you must translate that into a change in direction relative to their current orientation.
Often, the problem gives a sequence of moves or a set of people arranged in a line, circle, or grid, and asks you to determine who is where after the moves.

2. Key Points to Remember

#	Concept	How to Apply
1	Reference Frame	Decide on a fixed reference (e.g., North is up). If a person is facing North and turns right, they now face East.
2	Left & Right	Left = 90° counter‑clockwise, Right = 90° clockwise from the current facing direction.
3	U‑Turn	180° opposite direction.
4	Forward / Backward	Move along the current facing direction (forward) or opposite (backward).
5	Relative Positions	When two people move together, keep them in the same relation unless stated otherwise.
6	Circular Arrangements	Use modular arithmetic (e.g., 8 positions → 8‑person circle). Moving “to the right” means incrementing the index by 1 (mod 8).
7	Segments & Distances	If “two steps forward” is mentioned, treat each step as one unit; keep track of cumulative distance.
8	Direction Indicators	Use abbreviations: N, NE, E, SE, S, SW, W, NW.
9	Directional Changes in Multiple People	When a group turns, each member’s facing direction changes by the same amount.
10	Cross‑Referencing	Combine the above rules with other reasoning questions (e.g., seating arrangements, relative ages).

3. Worked Example

Problem
Seven officers (A, B, C, D, E, F, G) are standing in a straight line facing East.

A turns left, B turns right, C turns 180°.

Then the whole group moves two steps forward in the direction they are now facing.

Finally, G turns right, and the whole group moves one step backward.

Question: After all the moves, which officer is at the farthest position to the East of the original line?

Step‑by‑Step Solution

Step	Action	Resulting Facing Direction
Initial	All face East	E
1. Individual Turns	A → left (from E) → North	A: N, B: E, C: W (180°), D: E, E: E, F: E, G: E
2. Group Move (2 steps forward)	Every officer moves 2 units in their current facing direction	Position shifts: • A: 0 E, 2 N • B: 2 E, 0 N • C: 0 E, –2 N • D: 2 E, 0 N • E: 2 E, 0 N • F: 2 E, 0 N • G: 2 E, 0 N
3. G turns right	G faces South (from E)	G: S
4. Group Move (1 step backward)	Move 1 unit opposite to each officer’s facing direction	New positions: • A: 0 E, 1 N (backward from N) • B: 1 E, 0 N (backward from E) • C: 0 E, –1 N (backward from W) • D: 1 E, 0 N • E: 1 E, 0 N • F: 1 E, 0 N • G: 1 E, –1 N (backward from S)

Identify Farthest Eastward Officer

Eastward coordinate = number of units moved East.
A: 0 E, B: 1 E, C: 0 E, D: 1 E, E: 1 E, F: 1 E, G: 1 E.
All B, D, E, F, G are equally farthest to the East (1 E).
Answer: Any of B, D, E, F, or G (the question may expect “B, D, E, F, G” or “five officers”).

4. Quick Revision Summary

Topic	Take‑away
Reference Frame	Pick North as “up”; keep it fixed.
Left / Right	90° turn counter‑clockwise / clockwise.
U‑Turn	180° opposite.
Forward / Backward	Move along or opposite to facing direction.
Group Moves	Everyone moves the same distance in the same relative direction.
Circular Movement	Use modulo arithmetic for positions.
Tracking	Write down facing direction after each turn; update positions stepwise.
Practice	Draw a quick diagram or use a table to avoid confusion.

Tip: When the problem is long, break it into sub‑steps, label each officer’s direction after every action, and keep a running tally of their