Reasoning

Coding-Decoding: Practice Questions with Answers

88 practice questions on Coding-Decoding, with answers; most also have an explanation or a worked solution. Try each one before you open its answer.

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1. Q.1

   In a certain code language, "pen is good" is written as "ab cd ef", and "good is costly" is written as "ef cd gh". What is the code for "costly" in this language?

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   Answer: gh

   Solution:

   1. "pen", "is", "good" code to "ab", "cd", "ef" (in order) in the first sentence; "good", "is", "costly" code to "ef", "cd", "gh" (in order) in the second.
   2. "is" and "good" are the words common to both sentences, and "cd" and "ef" are the codes common to both coded sentences — so together, {is, good} = {cd, ef}.
   3. "costly" is the only word in the second sentence that does not appear in the first, so its code must be the only code in the second sentence that does not appear among the first sentence’s codes.
   4. That code is "gh".

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2. Q.2

   In a certain code language, CAT is written as DBU. How will DOG be written in that language?

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   Answer: EPH

   Solution:

   1. Compare each letter: C→D, A→B, T→U — every letter has shifted forward by exactly 1 place in the alphabet.
   2. Apply the same +1 shift to D, O, G: D→E, O→P, G→H.

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3. Q.3

   In a code, each letter of a word is replaced by the letter that is the same distance from the end of the alphabet as the original letter is from the start (A↔Z, B↔Y, C↔X, and so on). How will FLOWER be coded?

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   Answer: UOLDVI

   Solution:

   1. Position from the start: F=6, L=12, O=15, W=23, E=5, R=18.
   2. Mirror position from the end: position p maps to (27 − p) — so F(6)→21=U, L(12)→15=O, O(15)→12=L, W(23)→4=D, E(5)→22=V, R(18)→9=I.
   3. Putting the coded letters together in order: U, O, L, D, V, I.

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4. Q.4

   In a certain code, ANT is written as BPW. Find the pattern (don't assume a constant shift — check every letter), then code DOG using the same pattern.

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   Answer: EQJ

   Solution:

   1. A→B is +1. N→P is +2. T→W is +3. The shift is NOT constant — it increases by 1 for each successive letter in the word (1st letter +1, 2nd +2, 3rd +3).
   2. Apply the same pattern to DOG: D (1st, +1) = E. O (2nd, +2) = Q. G (3rd, +3) = J.

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5. Q.5

   Using the rule from the first worked example (CAT→DBU, a +1 shift), verify the answer EPH for DOG by decoding it back with a −1 shift.

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   Answer: DOG (confirms the rule)

   Solution:

   1. Apply −1 to each letter of EPH: E→D, P→O, H→G.
   2. This gives back DOG exactly, confirming the +1 shift rule was applied correctly both ways.

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6. Q.6

   In a certain code, CAT is written as UBD. Find the rule, then code DOG using the same rule.

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   Answer: HPE

   Solution:

   1. A constant shift doesn't fit directly (C→U, A→B, T→D don't share one amount). Try reversing the letters first: CAT reversed is TAC.
   2. Now shift each letter of TAC by +1: T→U, A→B, C→D, giving UBD — this matches.
   3. Apply the same rule to DOG: reversed is GOD. Shift each by +1: G→H, O→P, D→E.

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7. Q.7

   In a code, each letter is replaced by its position number in the English alphabet (A=1, B=2, … Z=26), separated by hyphens. If WATER is coded as 23-1-20-5-18, how will EARTH be coded?

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   Answer: 5-1-18-20-8

   Solution:

   1. Position numbers: E=5, A=1, R=18, T=20, H=8.
   2. Writing these in order, separated by hyphens: 5-1-18-20-8.

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8. Q.8

   In a certain code, DOG is written as HPE (reverse the letters, then shift each by +1). Using the same rule, code CAT.

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   Answer: UBD. Reverse CAT to TAC, then shift each letter +1.

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9. Q.9

   Using the A=1, B=2, … Z=26 rule, how will the word MIND be coded?

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   Answer: 13-9-14-4

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10. Q.10

    In a certain code, BIG is written as CKJ. Find the pattern (the shift increases by one for each letter), then code CAT using the same pattern.

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    Answer: DCW. C(+1)=D, A(+2)=C, T(+3)=W.

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11. Q.11

    If PEN is coded as QFO (a +1 shift), verify this by decoding QFO back with a −1 shift.

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    Answer: PEN. Q−1=P, F−1=E, O−1=N — confirms the rule.

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12. Q.12

    Using the A=1, B=2, … Z=26 rule, how will the word BOAT be coded?

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    Answer: 2-15-1-20.

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13. Q.13

    Using the mirror rule from the worked examples (A↔Z, B↔Y, C↔X…), how will the word BRAIN be coded?

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    Answer: YIZRM

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14. Q.14

    Using the rule A=1, B=2, C=3, ... Z=26, how is GOLDEN coded (letters separated by hyphens)?

    1. A 7-15-12-4-5-14
    2. B 8-16-13-5-6-15
    3. C 14-5-4-12-15-7
    4. D 7-15-12-4-5-15
    Show answer

    Correct answer: (A) 7-15-12-4-5-14

    Each letter is replaced by its position in the alphabet: G=7, O=15, L=12, D=4, E=5, N=14, giving 7-15-12-4-5-14.

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15. Q.15

    In a certain code, JUNGLE is written as PATMRK. Using the same rule, how is VICTORY written?

    1. A BOIZUXE
    2. B CPJAVYF
    3. C BOIZUEX
    4. D ANHYTWD
    Show answer

    Correct answer: (A) BOIZUXE

    Every letter in JUNGLE->PATMRK is shifted forward by 6 places. Applying the same +6 shift to VICTORY gives BOIZUXE.

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16. Q.16

    In a certain code, PLATFORM is written as TPEXJSVQ. Using the same rule, how is BUILDING written?

    1. A FYMPHMRK
    2. B GZNQINSL
    3. C FYMPHMKR
    4. D EXLOGLQJ
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    Correct answer: (A) FYMPHMRK

    Every letter in PLATFORM->TPEXJSVQ is shifted forward by 4 places. Applying the same +4 shift to BUILDING gives FYMPHMRK.

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17. Q.17

    In a certain code, CASTLE is written as GEWXPI. Using the same rule, how is VILLAGE written?

    1. A ZMPPEKI
    2. B ANQQFLJ
    3. C YLOODJH
    4. D EROOZTV
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    Correct answer: (A) ZMPPEKI

    Each letter shifts forward by 4 in the alphabet (C→G, ...). Applying the same +4 shift to VILLAGE gives ZMPPEKI.

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18. Q.18

    Using the rule A=1, B=2, C=3, ... Z=26, how is HONEY coded (letters separated by hyphens)?

    1. A 8-15-14-5-25
    2. B 9-16-15-6-26
    3. C 25-5-14-15-8
    4. D 7-14-13-4-24
    Show answer

    Correct answer: (A) 8-15-14-5-25

    Replacing each letter with its position in the alphabet: H=8, O=15, N=14, E=5, Y=25, giving 8-15-14-5-25.

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19. Q.19

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), how is MARKET coded?

    1. A NZIPVG
    2. B GVPIZN
    3. C NBSLFU
    4. D OAJQWH
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    Correct answer: (A) NZIPVG

    Each letter is replaced by its mirror partner from the opposite end of the alphabet (A<->Z, B<->Y, ...), giving MARKET -> NZIPVG.

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20. Q.20

    Using the rule A=1, B=2, C=3, ... Z=26, how is JOURNEY coded (letters separated by hyphens)?

    1. A 10-15-21-18-14-5-25
    2. B 11-16-22-19-15-6-26
    3. C 9-14-20-17-13-4-24
    4. D 25-5-14-18-21-15-10
    Show answer

    Correct answer: (A) 10-15-21-18-14-5-25

    Replacing each letter with its position in the alphabet gives 10-15-21-18-14-5-25.

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21. Q.21

    In a certain code, COMET is written as DQNGU, where letters in odd positions (1st, 3rd, 5th...) shift forward by 1 and letters in even positions (2nd, 4th, 6th...) shift forward by 2. Using the same rule, how is NEBULA written?

    1. A OGCWMC
    2. B OGCWMD
    3. C OGCXMC
    4. D OHCWMC
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    Correct answer: (A) OGCWMC

    Odd positions shift by +1 and even positions shift by +2. Applying this to NEBULA gives OGCWMC.

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22. Q.22

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), how is WINTER coded?

    1. A DRMGVI
    2. B IVGMRD
    3. C XJOUFS
    4. D ESNHWJ
    Show answer

    Correct answer: (A) DRMGVI

    Each letter is replaced by its mirror partner from the opposite end of the alphabet (A<->Z, B<->Y, ...), giving WINTER -> DRMGVI.

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23. Q.23

    In a certain code, BOOK is written as DQQM. Using the same rule, how will PAGE be coded?

    1. A RCIG
    2. B RBHF
    3. C QCIG
    4. D RCHG
    Show answer

    Correct answer: (A) RCIG

    Every letter shifts forward by 2 (B->D, O->Q, O->Q, K->M). Applying +2 to PAGE: R, C, I, G.

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24. Q.24

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), EMERALD is coded as VNVIZOW. How is SAPPHIRE coded?

    1. A HZKKSRIV
    2. B HZKKSRIW
    3. C HZKKSRVI
    4. D HZKKRSIV
    Show answer

    Correct answer: (A) HZKKSRIV

    Each letter is replaced by its mirror partner in the alphabet (A<->Z, B<->Y, ...). Applying this to SAPPHIRE gives HZKKSRIV.

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25. Q.25

    In a certain code, MARKET is written as OCTMGV. Using the same rule, how is TRAFFIC written?

    1. A VTCHHKE
    2. B WUDIILF
    3. C USBGGJD
    4. D GIZUURX
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    Correct answer: (A) VTCHHKE

    Each letter shifts forward by 2 in the alphabet (M→O, ...). Applying the same +2 shift to TRAFFIC gives VTCHHKE.

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26. Q.26

    Using the rule A=1, B=2, C=3, ... Z=26, how is QUICK coded (letters separated by hyphens)?

    1. A 17-21-9-3-11
    2. B 18-22-10-4-12
    3. C 11-3-9-21-17
    4. D 16-20-8-2-10
    Show answer

    Correct answer: (A) 17-21-9-3-11

    Replacing each letter with its position in the alphabet: Q=17, U=21, I=9, C=3, K=11, giving 17-21-9-3-11.

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27. Q.27

    In a certain code, GRAPE is written as KVETI. Using the same rule, how is LEMON written?

    1. A PIQSR
    2. B QJRTS
    3. C RKSUT
    4. D SLTVU
    Show answer

    Correct answer: (A) PIQSR

    Each letter shifts forward by 4 in the alphabet (G→K, ...). Applying the same +4 shift to LEMON gives PIQSR.

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28. Q.28

    Using the rule A=1, B=2, C=3, ... Z=26, how is THUNDER coded (letters separated by hyphens)?

    1. A 20-8-21-14-4-5-18
    2. B 20-8-21-14-4-5-19
    3. C 20-9-21-14-4-5-18
    4. D 21-8-21-14-4-5-18
    Show answer

    Correct answer: (A) 20-8-21-14-4-5-18

    Each letter is replaced by its position in the alphabet: T=20, H=8, U=21, N=14, D=4, E=5, R=18, giving 20-8-21-14-4-5-18.

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29. Q.29

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), how is METEOR coded?

    1. A NVGVLI
    2. B NVGVLJ
    3. C NVGWLI
    4. D NUGVLI
    Show answer

    Correct answer: (A) NVGVLI

    Each letter is replaced by its mirror partner in the alphabet; applying this to METEOR gives NVGVLI.

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30. Q.30

    Using the rule A=1, B=2, C=3, ... Z=26, how is PEACE coded (letters separated by hyphens)?

    1. A 16-5-1-3-5
    2. B 17-6-2-4-6
    3. C 5-3-1-5-16
    4. D 15-4-0-2-4
    Show answer

    Correct answer: (A) 16-5-1-3-5

    Replacing each letter with its position in the alphabet: P=16, E=5, A=1, C=3, E=5, giving 16-5-1-3-5.

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31. Q.31

    In a certain code, CHAIR is written as HMFNW. Using the same rule, how is CHALK written?

    1. A HMFQP
    2. B INGRQ
    3. C JOHSR
    4. D KPITS
    Show answer

    Correct answer: (A) HMFQP

    Each letter shifts forward by 5 in the alphabet (C→H, ...). Applying the same +5 shift to CHALK gives HMFQP.

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32. Q.32

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), JOURNEY is coded as QLFIMVB. How is JASMINE coded?

    1. A QZHNRMV
    2. B VMRNHZQ
    3. C QZHNRMW
    4. D KBTNJOF
    Show answer

    Correct answer: (A) QZHNRMV

    Each letter is replaced by its mirror partner in the alphabet (A<->Z, B<->Y, ...). Applying this to JASMINE gives QZHNRMV.

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33. Q.33

    In a certain code, APPLE is written as ETTPI. Using the same rule, how is MANGO written?

    1. A QERKS
    2. B RFSLT
    3. C SGTMU
    4. D THUNV
    Show answer

    Correct answer: (A) QERKS

    Each letter shifts forward by 4 in the alphabet (A→E, ...). Applying the same +4 shift to MANGO gives QERKS.

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34. Q.34

    In a certain code, TRAIN is written as YWFNS. Using the same rule, how is GHOST written?

    1. A LMTXY
    2. B MNUYZ
    3. C NOVZA
    4. D OPWAB
    Show answer

    Correct answer: (A) LMTXY

    Each letter shifts forward by 5 in the alphabet (T→Y, ...). Applying the same +5 shift to GHOST gives LMTXY.

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35. Q.35

    In a certain code, WATER is written as XBUFS. Using the same rule, how is STONE written?

    1. A TUPOF
    2. B UVQPG
    3. C VWRQH
    4. D WXSRI
    Show answer

    Correct answer: (A) TUPOF

    Each letter shifts forward by 1 in the alphabet (W→X, ...). Applying the same +1 shift to STONE gives TUPOF.

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36. Q.36

    In a certain code, PLANT is written as UQFSY. Using the same rule, how is QUEEN written?

    1. A VZJJS
    2. B WAKKT
    3. C XBLLU
    4. D YCMMV
    Show answer

    Correct answer: (A) VZJJS

    Each letter shifts forward by 5 in the alphabet (P→U, ...). Applying the same +5 shift to QUEEN gives VZJJS.

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37. Q.37

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), LANTERN is coded as OZMGVIM. How is CRYSTAL coded?

    1. A XIBHGZO
    2. B XIBHGZP
    3. C XIBGHZO
    4. D XJBHGZO
    Show answer

    Correct answer: (A) XIBHGZO

    Each letter is replaced by its mirror partner in the alphabet (A<->Z, B<->Y, ...). Applying this to CRYSTAL gives XIBHGZO.

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38. Q.38

    Using the rule A=1, B=2, C=3, ... Z=26, how is BRAVE coded (letters separated by hyphens)?

    1. A 2-18-1-22-5
    2. B 3-19-2-23-6
    3. C 5-22-1-18-2
    4. D 1-17-0-21-4
    Show answer

    Correct answer: (A) 2-18-1-22-5

    Replacing each letter with its position in the alphabet: B=2, R=18, A=1, V=22, E=5, giving 2-18-1-22-5.

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39. Q.39

    In a certain code, BRIDGE is written as DTKFIG. Using the same rule, how is FOREST written?

    1. A HQTGUV
    2. B IRUHVW
    3. C GPSFTU
    4. D ULIVHG
    Show answer

    Correct answer: (A) HQTGUV

    Each letter shifts forward by 2 in the alphabet (B→D, ...). Applying the same +2 shift to FOREST gives HQTGUV.

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40. Q.40

    In a certain code, RIVER is written as TKXGT. Using the same rule, how is OCEAN written?

    1. A QEGCP
    2. B RFHDQ
    3. C SGIER
    4. D THJFS
    Show answer

    Correct answer: (A) QEGCP

    Each letter shifts forward by 2 in the alphabet (R→T, ...). Applying the same +2 shift to OCEAN gives QEGCP.

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41. Q.41

    In a certain code, GEYSER is written as IGAUGT. Using the same rule, how is AVALANCHE written?

    1. A CXCNCPEJG
    2. B CXCNCPEJH
    3. C CXCNCQEJG
    4. D CYCNCPEJG
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    Correct answer: (A) CXCNCPEJG

    In GEYSER->IGAUGT, each letter shifts forward by 2 places. Applying the same +2 shift to AVALANCHE gives CXCNCPEJG.

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42. Q.42

    In a certain code, CABINET is written as IGHOTKZ. Using the same rule, how is FESTIVAL written?

    1. A LKYZOBGR
    2. B MLZAPCHS
    3. C KJXYNAFQ
    4. D UVHGREZO
    Show answer

    Correct answer: (A) LKYZOBGR

    Each letter shifts forward by 6 in the alphabet (C→I, ...). Applying the same +6 shift to FESTIVAL gives LKYZOBGR.

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43. Q.43

    Using the mirror-alphabet rule (A<->Z, B<->Y, C<->X, and so on), how is KITCHEN coded?

    1. A PRGXSVM
    2. B LJUDIFO
    3. C JHSBGDM
    4. D MVSXGRP
    Show answer

    Correct answer: (A) PRGXSVM

    Each letter is replaced by its mirror partner in the alphabet (A<->Z, B<->Y, ...), giving PRGXSVM.

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44. Q.44

    Using the rule A=1, B=2, C=3, ... Z=26, how is FALCON coded (letters separated by hyphens)?

    1. A 6-1-12-3-15-14
    2. B 6-1-12-3-15-13
    3. C 6-1-13-3-15-14
    4. D 5-1-12-3-15-14
    Show answer

    Correct answer: (A) 6-1-12-3-15-14

    Each letter is replaced by its position in the alphabet: F=6, A=1, L=12, C=3, O=15, N=14, giving 6-1-12-3-15-14.

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45. Q.45

    In a certain code language, CAT is written as DBU. How will DOG be written?

    1. A EPH
    2. B EQI
    3. C FQI
    4. D DPH
    Show answer

    Correct answer: (A) EPH

    Every letter in CAT->DBU shifted +1. Applying the same shift to D, O, G: E, P, H.

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46. Q.46

    In a certain code, TUNDRA is written as VVPETB, where letters in odd positions (1st, 3rd, 5th...) shift forward by 2 and letters in even positions (2nd, 4th, 6th...) shift forward by 1. Using the same rule, how is PLATEAU written?

    1. A RMCUGBW
    2. B RMCUGBV
    3. C RMBUGBW
    4. D RLCUGBW
    Show answer

    Correct answer: (A) RMCUGBW

    Odd-position letters shift by +2 and even-position letters shift by +1. Applying this to PLATEAU gives RMCUGBW.

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47. Q.47

    Using the rule A=1, B=2, C=3, ... Z=26, how is SILENT coded (letters separated by hyphens)?

    1. A 19-9-12-5-14-20
    2. B 20-10-13-6-15-21
    3. C 20-14-5-12-9-19
    4. D 19-9-12-5-14-21
    Show answer

    Correct answer: (A) 19-9-12-5-14-20

    Each letter is replaced by its position in the alphabet: S=19, I=9, L=12, E=5, N=14, T=20, giving 19-9-12-5-14-20.

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48. Q.48

    In a certain code, CHICKEN is written as JOPJRLU. Using the same rule, how is WHISTLE written?

    1. A DOPZASL
    2. B EPQABTM
    3. C DOPZALS
    4. D CNOYZRK
    Show answer

    Correct answer: (A) DOPZASL

    Every letter in CHICKEN->JOPJRLU is shifted forward by 7 places. Applying the same +7 shift to WHISTLE gives DOPZASL.

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49. Q.49

    In a certain code, DAWN is written as FBYO, where letters in odd positions (1st, 3rd...) shift forward by 2 and letters in even positions (2nd, 4th...) shift forward by 1. Using the same rule, how is TWILIGHT written?

    1. A VXKMKHJU
    2. B VXKMKHJV
    3. C VXKMKHIU
    4. D VYKMKHJU
    Show answer

    Correct answer: (A) VXKMKHJU

    Odd positions shift by +2 and even positions shift by +1. Applying this to TWILIGHT gives VXKMKHJU.

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50. Q.50

    Using a reverse-alphabet code (A<->Z, B<->Y, C<->X...), how is FLOWER coded?

    1. A UOLDVI
    2. B ULOVDI
    3. C VOLDUI
    4. D UOLVDI
    Show answer

    Correct answer: (A) UOLDVI

    Each position p maps to (27−p): F(6)->U(21), L(12)->O(15), O(15)->L(12), W(23)->D(4), E(5)->V(22), R(18)->I(9).

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