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4th Std Scholarship · Intelligence Test

Coding-Decoding

5 concepts · 40 practice questions with answers · Free to read

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Letter codes : shifting forward or backward

From daily life

Friends play a game to write secret messages : write the next letter in place of each letter. "CAT" becomes "DBU". Only someone who knows the rule can read the message. This is a code.

Simple definition

A code is a secret way of writing a word. To decode is to turn the code back into the plain word. Here every letter moves a fixed number of steps forward (+) or backward (−). After Z comes A again.

Live figure

Letter codes : shifting forward or backward

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Example of shifting (+1)

Original wordLettersNew lettersCode
CATC, A, TD, B, UDBU
DOGD, O, GE, P, HEPH
XYZX, Y, ZY, Z, AYZA
1
Rule 1

Shift every letter by the same number of steps. The shift is the same for all letters.

  • E.g. "CAT" 1 step forward : C→D, A→B, T→U. Code DBU.
2
Rule 2

To find the steps, look at the first pair of letters : number of the code letter − number of the original letter.

  • E.g. "BAT = DCV". B (2) → D (4). Steps +2.
3
Rule 3

To decode go the opposite way : subtract the steps from the code.

  • E.g. +3 code "KRXVH" : K−3 = H, R−3 = O, X−3 = U, V−3 = S, H−3 = E. The word is HOUSE.
4
Rule 4

Going beyond Z you come back to A; going back from A you come to Z.

  • E.g. "XYZ" +3 : X→A, Y→B, Z→C. Code ABC.
Example 1 · easy

If every letter is shifted 1 step forward, what is the code of "MANGO"?

  1. M→N, A→B, N→O, G→H, O→P.
  2. Answer : NBOHP.
Example 2 · medium

In a code "PEN" = "RGP". In the same code what is "INK"?

  1. P→R, E→G, N→P. Steps +2.
  2. I→K, N→P, K→M. Answer : KPM.
Example 3 · exam type

In a code "SUN" = "VXQ". In the same code what does "KRXVH" mean?

  1. S→V, U→X, N→Q. Steps +3.
  2. Decode : K−3 = H, R−3 = O, X−3 = U, V−3 = S, H−3 = E. Answer : HOUSE.
Remember

Look at the first code letter and the first original letter to get the steps; then the same rule everywhere.

Common mistake

Going forward again while decoding. If the code was made by shifting forward, go backward to decode.

Shortcut

Memory clue : "Code forward, decode backward."

Shortcut

When letters near Z come, use numbers : if the number goes above 26, subtract 26.

Spot the difference

SituationWhat to do
Word given, code wantedShift the letters forward (the given steps)
Code given, word wantedShift the letters backward
Steps not knownFind them from one pair

Practice questions

Easy
  1. 1If every letter is shifted 1 step forward, what is the code of "CAT"?
  2. 2If every letter is shifted 2 steps forward, what is the code of "BOX"?
  3. 3If every letter is shifted 1 step backward, what is the code of "DOG"?
Medium
  1. 4In a code "BAG" = "DCI". In the same code what is "MAP"?
  2. 5What does the +3 code "KHOOR" mean?
  3. 6In the +3 code what is the code of "XYZ"?
Challenging
  1. 7In the +1 code what is the code of "ZOO"?
  2. 8In a code "FAN" = "HCP". In the same code what does "JCV" mean?
Show answers (try them yourself first)
  1. 1DBU.
  2. 2DQZ.
  3. 3CNF.
  4. 4B→D, A→C, G→I. Steps +2. MAP : M→O, A→C, P→R. Answer : OCR.
  5. 5K−3 = H, H−3 = E, O−3 = L, O−3 = L, R−3 = O. Answer : HELLO.
  6. 6X→A, Y→B, Z→C. Answer : ABC.
  7. 7Z→A, O→P, O→P. Answer : APP.
  8. 8F→H, A→C, N→P : +2. J−2 = H, C−2 = A, V−2 = T. Answer : HAT.

Opposite letter code and reverse word

From daily life

In a mirror left becomes right. The alphabet can be seen like that too : in place of A comes Z, in place of B comes Y. And in a mirror a word looks reversed, which is also a code.

Simple definition

Opposite letter code : in place of every letter write its opposite letter (A↔Z, B↔Y, …). Number of the opposite letter = 27 − original number. Reverse word code : write the letters of the word in reverse order.

Pairs of opposite letters

OriginalOppositeOriginalOpposite
AZNM
BYOL
CXSH
EVTG
1
Rule 1

Opposite letter = the letter with number 27 − original number.

  • E.g. C (3) → 27 − 3 = 24 = X. A (1) → 26 = Z. T (20) → 7 = G. The code of "CAT" is XZG.
2
Rule 2

The opposite letter code works the same in both directions. So applying the same rule to the code gives the original word.

  • E.g. Opposite letters of XZG : X→C, Z→A, G→T. The word is CAT.
3
Rule 3

In a reverse word code the letters are the same, only the order is reversed.

  • E.g. The reverse word of "CAT" is "TAC".
4
Rule 4

To find which rule it is, look at the first letter : if A→Z, it is the opposite letter; if the letters are the same but the order is reversed, it is the reverse word.

  • E.g. "ABC = ZYX" is an opposite letter code; "ABC = CBA" is a reverse word code.
Example 1 · easy

In the opposite letter code what is the code of "BAG"?

  1. B (2) → 25 = Y, A → Z, G (7) → 20 = T.
  2. Answer : YZT.
Example 2 · medium

In the opposite letter code what is the code of "DOG"?

  1. D (4) → 23 = W, O (15) → 12 = L, G (7) → 20 = T.
  2. Answer : WLT.
Example 3 · exam type

In a code "MAP" = "NZK". In the same code what is "SUN"?

  1. M (13) → N (14), A → Z, P (16) → K (11). This is the opposite letter code.
  2. S (19) → 8 = H, U (21) → 6 = F, N (14) → 13 = M. Answer : HFM.
Remember

In the opposite letter code you can recognise it at once from the first pair : A and Z, M and N, B and Y.

Common mistake

Using 26 − number to find the opposite letter. The right way is 27 − number.

Shortcut

Memory clue : "27 minus the number."

Shortcut

M and N are opposites of each other; so MN is in the middle. They come as a pair between the two halves A to M and N to Z.

Spot the difference

CodeWord "CAT"How to recognise it
Opposite letterXZGZ in place of A
Reverse wordTACSame letters, reverse order
+1 forwardDBUEvery letter is the next one

Practice questions

Easy
  1. 1In the opposite letter code what is the code of "AB"?
  2. 2In the opposite letter code what does "ZYX" mean?
  3. 3What is the reverse word code of "STOP"?
Medium
  1. 4In the opposite letter code what is the code of "TEN"?
  2. 5In the opposite letter code what does "OLEV" mean?
  3. 6What is the reverse word code of "MARKET"?
Challenging
  1. 7In a code "HOME" = "SLNV". In the same code what is "ROSE"?
  2. 8In a code the word is first reversed and then each letter is changed to its opposite letter. What is the code of "CAT"?
Show answers (try them yourself first)
  1. 1A→Z, B→Y. Answer : ZY.
  2. 2Z→A, Y→B, X→C. Answer : ABC.
  3. 3POTS.
  4. 4T→G, E→V, N→M. Answer : GVM.
  5. 5O→L, L→O, E→V, V→E. Answer : LOVE.
  6. 6TEKRAM.
  7. 7H→S, O→L, M→N, E→V : the opposite letter code. R (18) → 9 = I, O → L, S (19) → 8 = H, E → V. Answer : ILHV.
  8. 8Reversed word : TAC. Then T (20) → 7 = G, A → Z, C (3) → 24 = X. Answer : GZX.

Letter = number : number codes

From daily life

In a row every student has a roll number. The letters A to Z also have numbers : A = 1, B = 2, … Z = 26. Using the numbers of the letters of a word we can make a number code.

Simple definition

Number code : write the number of each letter in its place. The value of a word is the sum of the numbers of its letters.

Numbers of letters

LetterNumberLetterNumber
A1O15
E5T20
J10Y25
1
Rule 1

Letter = number. The code of a word is a row of numbers.

  • E.g. "CAT" = 3 - 1 - 20.
2
Rule 2

Value of a word = sum of the numbers of all its letters.

  • E.g. "CAB" = 3 + 1 + 2 = 6.
3
Rule 3

If a code is given, find the letter for each number. Use the EJOTY landmarks.

  • E.g. 8 - 5 - 12 - 16 : H, E, L, P. The word is "HELP".
4
Rule 4

If the sum and one letter are given, subtract to find the other letter.

  • E.g. Value of two letters is 27 and one letter is Z (26). The other is 27 − 26 = 1, that is A.
Example 1 · easy

What is the value of "DOG"?

  1. D = 4, O = 15, G = 7.
  2. 4 + 15 + 7 = 26.
Example 2 · medium

What is the number code of "FISH"?

  1. F = 6, I = 9, S = 19, H = 8.
  2. Answer : 6 - 9 - 19 - 8.
Example 3 · exam type

What does the code 3 - 15 - 13 - 5 mean?

  1. 3 = C, 15 = O, 13 = M, 5 = E.
  2. Answer : COME.
Remember

Keep the EJOTY landmarks (5, 10, 15, 20, 25) in mind and the numbers come quickly.

Common mistake

Reading a two-digit number as two letters (e.g. reading 12 as 1 and 2). In a code 12 means L.

Shortcut

Memory clue : "Letter = number; number = letter."

Shortcut

After finding the value of a word, add once more; if one letter was wrong, the sum is wrong.

Spot the difference

QuestionHow to solve it
Code of a wordWrite the number of each letter
Value of a wordSum of the numbers
Code given, word wantedFind the letter for each number

Practice questions

Easy
  1. 1What is the value of "BAG"?
  2. 2What is the number code of "CAB"?
  3. 3What does the code 1 - 2 - 3 mean?
Medium
  1. 4What is the value of "BOOK"?
  2. 5What does the code 19 - 21 - 14 mean?
  3. 6Which has the greater value : "AGE" or "EGG"?
Challenging
  1. 7What is the difference between the values of "CAT" and "DOG"?
  2. 8The value of two letters is 27 and one of them is Z. Which is the other letter?
Show answers (try them yourself first)
  1. 12 + 1 + 7 = 10.
  2. 23 - 1 - 2.
  3. 3ABC.
  4. 42 + 15 + 15 + 11 = 43.
  5. 519 = S, 21 = U, 14 = N. Answer : SUN.
  6. 6AGE = 1 + 7 + 5 = 13. EGG = 5 + 7 + 7 = 19. EGG is greater.
  7. 7CAT = 3 + 1 + 20 = 24. DOG = 26. The difference is 2.
  8. 827 − 26 = 1, that is A.

Swapping words and the common-word trick

From daily life

In a game we say, "From today let us call water milk." Then if someone asks, "What will you drink when thirsty?" the answer is "milk". The names change but the thing is the same.

Simple definition

In this code words are replaced by other words. In the question the thing stays the same, only its name changes. In the second kind, groups of letters are codes for sentences; by finding the common word in two sentences we can find the code of each word.

Chain of names

Real thingIts new name
RedBlue
BlueGreen
GreenYellow
YellowBlack
1
Rule 1

First recognise the real thing, then give its new name.

  • E.g. The real colour of the sky is blue. Blue is called green, so the answer is green.
2
Rule 2

A new name is not changed again. Change once and stop.

  • E.g. Sky = blue = green. Do not change "green" again into yellow.
3
Rule 3

If two sentences have a common word, the common code is the code of that word.

  • E.g. "pit mun" = red flower; "mun kal" = flower beautiful. Common code mun, common word flower. So flower = mun.
4
Rule 4

The order of the words in a sentence may be changed. Look at the common code, not the order.

  • E.g. "bu ka sa" and "ka ra". Common code ka.
Example 1 · easy

Red = blue, blue = green, green = yellow, yellow = black. What do they call the colour of the sky?

  1. The sky is really blue. Blue is called green.
  2. Answer : Green.
Example 2 · medium

In the same code what do they call the colour of grass?

  1. Grass is really green. Green is called yellow.
  2. Answer : Yellow.
Example 3 · exam type

"ka ra" = we school, "ra bu" = school go, "bu ka sa" = go we daily. What is the code of "daily"?

  1. First and second sentences : common ra, so school = ra. Second and third : common bu, so go = bu.
  2. First and third : common ka, so we = ka.
  3. The one left in the third sentence is sa = daily. Answer : sa.
Remember

The name changes, the thing does not. First the real thing, then the new name.

Common mistake

Changing the name twice. Stop at the new name you have.

Shortcut

Memory clue : "Real thing, new name; common word, common code."

Shortcut

If each word comes only once in three sentences, recognise and remove all the other words; the one left over is the one wanted.

Spot the difference

QuestionHow to solve it
The name is changedReal thing, then its new name
Two sentences, one common wordCommon word = common code
Three sentencesJoin the pairs and separate the words one by one

Practice questions

Easy
  1. 1If night is called day and day is called night, what will they say when we sleep?
  2. 2In the same code what will they say when the sun is seen?
  3. 3"pit mun" = red flower, "mun kal" = flower beautiful. What is the code of "red"?
Medium
  1. 4In the same code what is the code of "beautiful"?
  2. 5"ta mi" = I eat, "mi lo" = eat fruit. What is the code of "fruit"?
  3. 6If an apple is called a mango and a mango is called a banana, what is a mango called?
Challenging
  1. 7"ba ro" = he plays, "di ba" = ball he, "ma di" = red ball. What is the code of "plays"?
  2. 8Red = blue, blue = green, green = yellow, yellow = black. What do they call the colour of a sunflower?
Show answers (try them yourself first)
  1. 1Sleep comes at night. Night is called day. Answer : Day.
  2. 2The sun is seen in the day. Day is called night. Answer : Night.
  3. 3pit.
  4. 4kal.
  5. 5mi is in both sentences. mi = eat. Then lo = fruit. Answer : lo.
  6. 6A mango is called a banana. Answer : Banana.
  7. 7ba is in two sentences (he), di is in two sentences (ball). ro = plays, so the answer : ro.
  8. 8A sunflower is really yellow. Yellow is called black. Answer : Black.

Mixed codes : alternate, growing steps and swapping pairs

From daily life

Climbing stairs, sometimes we climb one step, sometimes two. In some codes too the steps of each letter are different. Once the rule is understood, every letter can be solved.

Simple definition

In a mixed code the rule changes with the letter : alternate (+1, −1, +1, −1), growing steps (+1, +2, +3, +4) or swapping pairs (two neighbouring letters exchange places). To find the rule check two or three letters.

Examples of mixed codes

WordRuleCode
BOAT+1, −1, +1, −1CNBS
BEAT+1, +2, +3, +4CGDX
BOOKSwapping pairsOBKO
1
Rule 1

Alternate : the first and third letters by one rule; the second and fourth by another.

  • E.g. BOAT : B+1 = C, O−1 = N, A+1 = B, T−1 = S. Code CNBS.
2
Rule 2

Growing steps : one more step for each next letter.

  • E.g. BEAT : B+1 = C, E+2 = G, A+3 = D, T+4 = X. Code CGDX.
3
Rule 3

Swapping pairs : the first and second letters exchange places, the third and fourth exchange places.

  • E.g. BOOK : (B, O) → O, B and (O, K) → K, O. Code OBKO.
4
Rule 4

Frame to find the rule : (1) Find the steps of each letter of the given pair. (2) If all steps are the same it is a simple code, if different it is mixed. (3) Apply the same rule to the next word. (4) Check the answer.

  • E.g. MAKE = OZMD : M→O (+2), A→Z (−1), K→M (+2), E→D (−1). So alternate +2, −1.
Example 1 · easy

With the alternate rule +1, −1, what is the code of "ROW"?

  1. R+1 = S, O−1 = N, W+1 = X.
  2. Answer : SNX.
Example 2 · medium

With growing steps (+1, +2, +3, +4), what is the code of "PLAN"?

  1. P+1 = Q, L+2 = N, A+3 = D, N+4 = R.
  2. Answer : QNDR.
Example 3 · exam type

In a code "MAKE" = "OZMD". In the same code what is "LION"?

  1. MAKE : +2, −1, +2, −1.
  2. LION : L+2 = N, I−1 = H, O+2 = Q, N−1 = M. Answer : NHQM.
Remember

When solving a mixed code check the steps of each letter separately. Do not fix the rule from one letter.

Common mistake

Applying the rule of the first letter to all letters. If the second letter is not checked, the alternate rule is not seen.

Shortcut

Memory clue : "Check the steps of every letter."

Shortcut

At the end count the letters of the answer : the code must have as many letters as the word.

Spot the difference

SignRule
All steps the sameSimple code
Steps alternateAlternate code
Steps grow 1, 2, 3 …Growing steps
Same letters, places changedSwapping code

Practice questions

Easy
  1. 1With the alternate rule +1, −1, what is the code of "FUN"?
  2. 2With swapping pairs, what is the code of "BOOK"?
  3. 3With growing steps (+1, +2, +3), what is the code of "MAP"?
Medium
  1. 4With growing steps (+1, +2, +3, +4), what is the code of "SAND"?
  2. 5What does the alternate +1, −1 code "CNBS" mean?
  3. 6With swapping pairs, what is the code of "TEAM"?
Challenging
  1. 7In a code "HAND" = "KZQC". In the same code what is "FOOT"?
  2. 8First swapping pairs, then every letter +1. What is the code of "PLAY"?
Show answers (try them yourself first)
  1. 1F+1 = G, U−1 = T, N+1 = O. Answer : GTO.
  2. 2OBKO.
  3. 3M+1 = N, A+2 = C, P+3 = S. Answer : NCS.
  4. 4S+1 = T, A+2 = C, N+3 = Q, D+4 = H. Answer : TCQH.
  5. 5C−1 = B, N+1 = O, B−1 = A, S+1 = T. Answer : BOAT.
  6. 6(T, E) → E, T and (A, M) → M, A. Answer : ETMA.
  7. 7H→K (+3), A→Z (−1), N→Q (+3), D→C (−1). FOOT : F+3 = I, O−1 = N, O+3 = R, T−1 = S. Answer : INRS.
  8. 8Swapping pairs : LPYA. Each +1 : L→M, P→Q, Y→Z, A→B. Answer : MQZB.

Quick revision of the whole lesson

TypeMemory clue
Shifting forward or backwardCode forward, decode backward
Opposite letter27 minus the number
Letter = numberLetter = number; number = letter
Swapping wordsReal thing, new name
Common wordCommon word, common code
Mixed codesCheck the steps of every letter

🎯 Most important points for the exam

  • In a code find by numbers how many steps each letter moved.
  • After Z comes A, and going back from A you reach Z.
  • Opposite letter = 27 − number.
  • Value of a word = sum of the numbers of its letters (A = 1, B = 2 …).
  • If names are changed, first the real thing, then its new name; change the name only once.
  • The common code of two sentences is the common word.
  • In a mixed code check the steps of all the letters.
🧠 Study mantra

"Count the steps, find the rule; check at the end."