2.2 Coding, Series & Direction Sense

2.2 Coding, Series & Direction Sense

Quick Answer: Coding questions hide a fixed transformation; series questions hide a fixed step pattern; direction questions hide a path on a compass plane. In each case, discover the rule from what is given, apply it once cleanly, and refuse any option that requires a second, different rule.

Coding-decoding, series, and direction sense appear alongside word analogies in many PAF initial intelligence papers. They reward mechanical accuracy more than English literature skill. For Aeronautical Engineering candidates, treat them like short applied-math drills: define the mapping, advance the sequence, or resolve the vector walk. Again, coaching chatter often cites roughly 100 questions in ~35 minutes for the intelligence block—use that only as a speed hedge, not as an official blueprint.

Letter Coding — Build the Map

A coding item usually states: If MASTER is coded as …, how is THRUST coded? Your job is to reverse-engineer the map.

Common maps:

Alphabet position reminder (memorise once): A=1 … M=13 … Z=26. Opposite letter of position n is position (27 − n).

Worked example — constant shift

If COLD is written as DPME, each letter moved +1. Then HEAT → IFBU.

Worked example — reverse + shift

If PILOT is coded as TOLIP (simple reverse), then WINGS → SGNIW. If the code were UQNPS for PILOT, that is reverse then +1 (or +1 then reverse—verify both orders on the example before applying).

Worked example — opposite letters

AC → ZX because A↔Z, C↔X. Then BD → YW.

Number / Symbol Coding

Sometimes words map to numbers: If ENGINE = 48, count letters, sum positions, or multiply counts. Procedure:

1. Count letters; compare to the number.
2. Sum alphabetical positions; compare.
3. Try vowels-only or consonants-only sums.
4. Only after the example fits uniquely should you code the target word.

Worked example

Suppose SKY = 55 because 19+11+25 = 55. Then AIR = 1+9+18 = 28. If instead SKY = 3, the code was letter count—then AIR = 3 as well. Always distinguish sum codes from count codes.

Series Completion — Smallest Consistent Pattern

Series may be letters, numbers, or mixed.

Number series patterns to try in order:

1. Constant difference (arithmetic): 7, 10, 13, 16, ? → +3 → 19
2. Constant multiplier: 2, 6, 18, 54, ? → ×3 → 162
3. Growing difference: 2, 3, 5, 8, 12, ? → +1,+2,+3,+4 → next +5 → 17
4. Alternating two series interleaved: 3, 8, 5, 10, 7, 12, ? → odd terms +2, even +2 → next odd 9
5. Squares/cubes nearby: 8, 27, 64, 125, ? → 2³,3³,4³,5³ → 216 (6³)

Letter series patterns:

• Continuous shift: A, C, E, G, ? → +2 → I
• Two-pointer: A, Z, B, Y, C, ? → X
• Grouped: ABC, EFG, IJK, ? → skip one letter between groups → MNO

Worked example — mixed

A2, C5, E8, G11, ? → letters +2, numbers +3 → I14.

Before choosing, recompute the last given term from your rule. If your rule cannot rebuild what is already printed, the rule is wrong.

Direction Sense — Compass Geometry

Standard exam compass (top of page = North unless stated):

        N
        |
   W ———+——— E
        |
        S

Facing and turns:

• Face North; turn right → face East; turn right again → South; and so on.
• Face North; turn left → West.
• “Turn around” / “retrace” usually means reverse facing 180°.

Displacement vs distance:

• Path length = sum of segments walked.
• Net displacement = straight-line distance from start to end (often via Pythagoras if east–west and north–south legs remain).

Worked example

A cadet walks 10 m North, 6 m East, 4 m South, then 6 m West. Where is he relative to start?

• Net North = 10 − 4 = 6 m North
• Net East = 6 − 6 = 0
• Position: 6 m North of start; path length = 10+6+4+6 = 26 m

Worked example — facing after turns

Starts facing East. Turns left, walks, turns left again. Facing after two left turns from East: East → North → West.

Worked example — shadow / sun tricks (when present)

If a question states morning sun and shadow direction, remember in the northern hemisphere morning sun is roughly East, so shadow falls roughly West—only use when the stem supplies that framing; do not force astronomy into plain turn problems.

Combining Skills Under Time Pressure

On a fast paper, coding and series are usually higher accuracy per second than long reading-comprehension stems—if you know the patterns. Direction items are accurate if you sketch; mental-only tracking of four turns is a common self-inflicted error.

Practical pacing tips (consistent with a commonly reported ~35-minute intelligence sitting):

• For coding: spend time on the example pair, almost none on re-checking after a clean map.
• For series: test arithmetic difference first; escalate only if needed.
• For direction: draw North once; mark the start with a dot; update facing with a small arrow.

AE-Flavoured Dressing Does Not Change the Rule

Stems may say runway, hangar, control tower, or taxiway instead of point A. The geometry is identical. Likewise, coding a word like THRUST or GLIDER still uses letter maps—not fluid-mechanics definitions.

Worked example — runway walk

From the hangar, a technician walks 50 m along the runway heading North, turns right to the apron for 30 m, turns right again 50 m. Net: 30 m East of start (North and South cancel), facing South.

Error Log Categories

When you miss an item in practice, tag it:

1. Shift arithmetic error (miscounted +2 as +3)
2. Order of operations (reversed before shifting, but example was shift then reverse)
3. Interleaved series mistaken for a single series
4. Turn from wrong facing
5. Distance reported when displacement was asked (or reverse)

Fixing the tagged habit beats grinding random volume.

Short Practice Set

1. If BEAR → CFBS (+1), then WING → XJOH.
2. Series: 5, 6, 9, 14, 21, ? → differences +1,+3,+5,+7 → next +9 → 30.
3. Letters: B, D, G, K, ? → +2,+3,+4 → next +5 → P.
4. Walk 3 km East, 4 km North — displacement from start: 5 km (3-4-5 triangle).

Coding, series, and direction sense are score stabilisers: they punish carelessness more than lack of “general knowledge.” Pair them with the analogy habits from Section 2.1 so you do not waste seconds rereading stems.