Letter Series Reasoning Questions
Letter series questions give a run of letters with a hidden pattern and ask for the next letter or the missing ones. Convert each letter to its alphabet position (A = 1 to Z = 26), find the gaps, and check for alternating or interleaved patterns. The alphabet wraps around after Z.
Letter series is the alphabet version of number series, and it shares its position-counting habits with coding-decoding and analogy questions.
What Are Letter Series Questions?
You see a sequence such as A, C, E, G and must find the next term, or you see a sequence with gaps and must fill them. Every series follows a rule, and the rule almost always shows up when you turn the letters into numbers and look at the gaps between neighbours.
Alphabet Positions You Should Know
| Letters | Positions |
|---|---|
| A to E | 1 to 5 |
| F to J | 6 to 10 |
| K to O | 11 to 15 |
| P to T | 16 to 20 |
| U to Y | 21 to 25 |
| Z | 26 |
A handy memory aid is EJOTY: E = 5, J = 10, O = 15, T = 20 and Y = 25. Two facts help in many questions:
- Opposite letters: a letter and its mirror from the other end add up to 27. The opposite of K (11) is P (16), and A and Z are opposites.
- Wrapping: if you count past Z, continue from A. X (24) plus 5 is 29, minus 26, which is 3, so the result is C.
Common Patterns
| Pattern | Example | What happens |
|---|---|---|
| Constant gap forward | A, C, E, G | +2 each time |
| Constant gap backward | Z, X, V, T | −2 each time |
| Growing gap | B, C, E, H | Gaps of +1, +2, +3, then +4 |
| Two interleaved series | A, Z, C, X, E, V | Odd terms go forward, even terms go backward |
| Letter groups | AB, DE, GH, JK | Each group moves by the same step |
| Repeating pattern with gaps | abc, bca, cab | The block rotates each time |
| Position questions | 5th to the left of M | Count along the alphabet |
A Step-by-Step Method
- Write the position number under each letter.
- Find the gap between each pair of neighbours.
- If the gaps are constant or growing, extend the pattern one step.
- If the gaps look random, split the series into its odd-numbered and even-numbered terms and check each on its own.
- For groups or repeating blocks, look at each position within the group separately.
- Check your answer by counting it back from the previous term, and remember the wrap past Z.
Solved Examples
1. A, C, E, G, ? Answer: I. Each letter moves two places forward, so after G (7) comes I (9).
2. Z, X, V, T, ? Answer: R. Each letter moves two places back, so after T (20) comes R (18).
3. B, C, E, H, ? Answer: L. The positions are 2, 3, 5, 8, so the gaps are 1, 2, 3 and the next gap is 4. H is 8, and 8 + 4 = 12, which is L.
4. A, Z, C, X, E, V, ?, ? Answer: G, T. The odd terms A, C, E move two places forward, so the next is G. The even terms Z, X, V move two places back, so the next is T.
5. AB, DE, GH, JK, ? Answer: MN. The first letters A, D, G, J move three places forward each time, giving M. The second letters B, E, H, K do the same, giving N.
6. a b c b _ a c a _ a b c Answer: c, b. The series is the block abc rotating one place to the left each time: abc, bca, cab, abc. So the missing letters are c in the second block (b-c-a) and b in the third (c-a-b).
7. Which letter is the 5th to the left of M, what is the opposite of K, and what is X + 5? Answer: H, P and C. M is 13 and 13 − 5 = 8, which is H. K is 11, and 27 − 11 = 16, which is P. X is 24, and 24 + 5 = 29, which wraps to 3, which is C.
Common Mistakes
- Forgetting to wrap past Z. Counting beyond 26 returns to A, so subtract 26.
- Counting positions inclusively or exclusively by mistake. “5th to the left of M” means five steps from M, not including M itself.
- Looking at the whole series when it is really two series. If the gaps look irregular, split into odd and even terms.
- Applying the first rule you spot. Check the rule against every pair before you extend it.
- Treating letter groups as single letters. Look at the first letters and the second letters of each group on their own.
Practice Questions
Try each on paper, then check the answer.
1. D, G, J, M, ? Answer: P. Each letter moves three places forward, and M (13) + 3 = 16, which is P.
2. Y, W, U, S, ? Answer: Q. Each letter moves two places back, and S (19) − 2 = 17, which is Q.
3. C, D, F, I, ? Answer: M. The gaps are 1, 2, 3, so the next gap is 4. I (9) + 4 = 13, which is M.
4. A, C, F, J, ? Answer: O. The gaps are 2, 3, 4, so the next gap is 5. J (10) + 5 = 15, which is O.
5. B, Y, D, W, F, U, ?, ? Answer: H, S. The odd terms B, D, F move two places forward, giving H. The even terms Y, W, U move two places back, giving S.
6. AB, CD, EF, GH, ? Answer: IJ. Each group starts two letters after the previous one, so the first letters A, C, E, G continue to I, and the second letters B, D, F, H continue to J.
7. Z, A, Y, B, X, C, ?, ? Answer: W, D. The odd terms Z, Y, X move one place back, giving W. The even terms A, B, C move one place forward, giving D.
8. Which letter is exactly in the middle of D and J, and which letter is the 4th to the right of P? Answer: G and T. D is 4 and J is 10, so the middle is 7, which is G. P is 16 and 16 + 4 = 20, which is T.
Frequently Asked Questions
What are letter series questions in reasoning?
They give a sequence of letters that follows a hidden rule and ask for the next letter or the missing ones. Converting the letters to alphabet positions usually reveals the rule.
How do I solve letter series questions quickly?
Write each letter’s position number, find the gaps between neighbours, and extend the pattern. If the gaps look irregular, split the series into odd and even terms and check each separately.
What are the common patterns in letter series?
A constant gap forward or backward, a growing gap, two interleaved series, letter groups that move by the same step, and repeating blocks that rotate.
How do I handle the wrap from Z back to A?
Subtract 26 from any position above 26. For example, X (24) plus 5 is 29, which wraps to 3, which is C.
What is the opposite letter of a given letter?
Subtract the letter’s position from 27. For example, the opposite of K (11) is P (16).
Which exams ask letter series questions?
They appear in the reasoning sections of many bank and SSC exams and in some placement tests.