Alphabet Series: Types, Methods and Examples
Alphabet series is an important topic in the reasoning and mental-ability paper of competitive examinations. In an alphabet series question, a sequence of letters is given that follows a hidden rule, and the candidate has to find the next letter, the missing letter or the wrong letter in the series. The rule is usually based on moving forward or backward through the alphabet, skipping a fixed number of letters, or increasing the gap between the letters step by step. The topic tests the candidate's familiarity with the alphabet and the ability to recognise a pattern quickly.
For candidates preparing for APSC, ADRE, Assam Police, SSC, Railway and similar examinations in Assam, alphabet series appears regularly in the reasoning section. This article gives a complete deep-study revision of alphabet series. It explains the basic vocabulary, the position values of the letters, the main types of series, the useful shortcuts, the step-by-step method of solving, the common mistakes and a practical preparation plan. Once the position values of the alphabet are memorised, alphabet series becomes a fast and reliable scoring topic.
Basic Terms
- Alphabet series: a sequence of letters arranged according to a definite rule.
- Position value: the serial number of a letter, A being 1 and Z being 26.
- Forward series: a series in which the letters move ahead in the alphabet.
- Backward series: a series in which the letters move back in the alphabet.
- Skip letter series: a series in which a fixed number of letters is skipped each time.
- Alternating series: a series in which two different patterns take turns.
- Opposite letter: the letter that is 27 minus the position value of a given letter.
- EJOTY: a shortcut in which E is 5, J is 10, O is 15, T is 20 and Y is 25.
- Letter group series: a series in which groups of letters are given instead of single letters.
- Wrong letter series: a series in which one letter is incorrect and must be found.
- Alphabet test: a question that involves arranging, comparing or counting letters.
- Missing letter: the letter that should replace a blank in the series.
Core Concepts and Shortcuts
- The position values run from A = 1 to Z = 26.
- Use EJOTY to find values quickly: E = 5, J = 10, O = 15, T = 20, Y = 25.
- The reverse values are obtained by subtracting from 27; for example, A has reverse value 26 and Z has reverse value 1.
- Opposite letter pairs always add up to 27, such as A-Z, B-Y, C-X and so on.
- In a forward series, the gap is added; in a backward series, the gap is subtracted.
- If the gaps increase by a fixed amount, the series is based on an increasing gap.
- In letter group series, the shift is applied to each letter of the group in the same way.
Forward and Backward Series
In a forward series, each letter is ahead of the previous one by a fixed number of places. For example, in the series A, C, E, G, I, each letter moves forward by two places, so the next letter is K. In the series B, E, H, K, N, each letter moves forward by three places, so the next letter is Q. A backward series moves in the reverse direction. In the series Z, X, V, T, R, each letter moves back by two places, so the next letter is P. Sometimes the same series is written with a gap that changes, as in A, B, D, G, K, where the gaps are 1, 2, 3 and 4, so the next gap is 5 and the next letter is P. Recognising whether the movement is forward or backward, and whether the gap is fixed or changing, is the first step in solving any alphabet series.
Skip Letter and Alternating Series
In a skip letter series, a fixed number of letters is skipped between consecutive terms. For example, in A, D, G, J, M, two letters are skipped each time, which means the gap is three. In A, F, K, P, U, the gap is five, since four letters are skipped between each pair. When the gaps themselves form a pattern, the series becomes more interesting, as in A, C, F, J, O, where the gaps are 2, 3, 4 and 5, and the next gap is 6, giving the next letter U. In an alternating series, two patterns take turns, as in A, Z, C, X, E, V, where the odd-placed letters move forward by two and the even-placed letters move back by two. Alternating series require the candidate to split the sequence into two parts, one for the odd positions and one for the even positions, before finding the rule.
Letter Group Series
In letter group series, groups of two or three letters are given, and the shift is applied to every letter of the group. For example, in the series AB, DE, GH, JK, each letter of the group moves forward by three, and the next group is MN. Sometimes the first letter of the group follows one rule and the second letter follows another, as in AZ, BY, CX, DW, where the first letter moves forward while the second moves backward, and both approach each other. In some questions, the letters within a group also have a fixed relation, such as a group in which the second letter is three places ahead of the first. To solve such questions, the candidate should write the position values below each letter and then compare each position of the group separately.
Steps to Solve an Alphabet Series
The method of solving an alphabet series is systematic. First, write the position values of the given letters below them, because the numbers make the rule visible. Second, find the difference between the position values of consecutive terms; a constant difference means a simple forward or backward series. Third, if the difference is not constant, check whether the differences themselves form a pattern, such as 2, 3, 4, 5. Fourth, if the series looks irregular, split it into odd and even positions and examine each part separately. Fifth, for letter groups, compare each position of the group on its own. Finally, confirm the answer by applying the rule once more to the last two terms. This approach solves almost every alphabet series question quickly and accurately.
Examination Trends
In competitive examinations, alphabet series questions most often use simple forward and backward series, skip letter series, increasing gap series and alternating series. Letter group series and missing letter questions are also common. Some papers use the alphabet test, in which letters must be arranged in a particular order, or words must be formed from given letters. Objective questions frequently ask the next letter, the missing letter or the wrong letter. Because the alphabet is fixed and the patterns are limited, candidates who memorise the position values and practise the types can answer these questions in a few seconds.
Common Mistakes to Avoid
- Do not count the letter itself when measuring the gap; count only the places moved.
- Do not forget the backward series; always check whether the letters are moving back.
- In an alternating series, do not treat the odd and even positions as one continuous pattern.
- Do not mix up the position value and the reverse value of a letter.
- In letter groups, do not apply the same rule to both letters without checking the second letter separately.
How to Prepare This Topic
Begin by memorising the position values of all twenty-six letters, using the EJOTY shortcut to recall E, J, O, T and Y quickly. Learn the opposite letter pairs, which always add up to twenty-seven. Then study each type of series separately, solving at least fifteen questions of each type so that the patterns become familiar. Practise writing the position values below the letters, because this turns the question into a simple number series. Finally, attempt previous years' question papers under timed conditions, and review every mistake so that the same error is not repeated in the examination.
Frequently Asked Questions
What is an alphabet series in reasoning?
An alphabet series is a sequence of letters arranged according to a hidden rule. The candidate has to find the next letter, the missing letter or the wrong letter by identifying whether the letters move forward or backward and by what gap.
What is the EJOTY shortcut?
EJOTY is a shortcut to remember position values quickly: E is 5, J is 10, O is 15, T is 20 and Y is 25. From these fixed points, the value of any nearby letter can be found at once.
How do I find the opposite letter of a given letter?
The opposite letter is found by subtracting the position value of the given letter from 27. For example, the opposite of A (1) is Z (26), and the opposite of C (3) is X (24).
How do I solve an alternating alphabet series?
Split the series into two parts, one containing the letters at odd positions and one containing the letters at even positions. Find the rule for each part separately, and then apply it to get the required letter.
How do I solve a letter group series?
Write the position values below every letter, then compare each position of the group on its own, such as all first letters together and all second letters together. Apply the rule found for each position to the last group to get the answer.