Alphanumeric Series in Reasoning: Letter and Number Series, Counting Questions and Tricks for SSC Exams

An alphanumeric series mixes letters, numbers and sometimes symbols, and the question asks for the missing term or a count based on a condition. The patterns are not hard, but they need practice and a method. This guide on alphanumeric series for SSC explains the common patterns, the position table, the counting type of questions, solved examples and practice questions with answers.

Alphabet Position Table

Remember the opposite-letter rule: the position of a letter from the left and the position of its opposite letter from the right add up to 27 (A and Z, B and Y, and so on).

Common Patterns in Alphanumeric Series

Counting Type Questions

In these questions a sequence of letters, numbers and symbols is given and you must count the elements that satisfy a condition, such as “how many consonants are immediately preceded by an odd number?”. The steps are:

1. Write the sequence and number its positions.
2. Mark the elements that satisfy the first part of the condition.
3. Check the neighbour (preceding or following) of each marked element.
4. Count carefully and do not count one element twice.

Solved Examples

Example 1. Find the next term: B, E, H, K, ?
The positions are 2, 5, 8, 11 (+3 each). The next is 14, which is N.

Example 2. Find the next term: 3, 8, 15, 24, 35, ?
The terms are n² − 1 for n = 2, 3, 4, 5, 6. The next is 7² − 1 = 48.

Example 3. Find the next term: B2, D4, G7, K11, ?
Letters move +2, +3, +4, so the next is +5: K → P. Numbers move +2, +3, +4, so +5: 11 → 16. The answer is P16.

Example 4. Z1, Y4, X9, W16, ?
Letters go backwards and numbers are squares, so V25.

Example 5. In the sequence 7 K 4 M 9 B 2 T 5 R 8 P 3, how many consonants are immediately preceded by an odd number?
K (preceded by 7, odd) ✓; M (4) no; B (9) ✓; T (2) no; R (5) ✓; P (8) no. The count is 3.

Example 6. In 4 A 6 E 3 I 8 B 2 U 5, how many even numbers are immediately followed by a vowel?
4 followed by A ✓; 6 by E ✓; 8 by B no; 2 by U ✓. The count is 3.

Tricks

• Convert the letters to numbers using the position table and look for the pattern in numbers.
• Check whether the letters and numbers follow separate patterns.
• Look for squares, cubes, primes and Fibonacci type patterns in the number part.
• In counting questions, circle the matching elements on paper.
• Check both the preceding and following conditions carefully, because the direction matters.

Quick Tips

• Convert letters to positions while solving.
• Check letters and numbers separately.
• Memorise squares up to 25 and cubes up to 10.
• Mark the matching elements in counting questions.

Quick Revision Points

• A = 1 to Z = 26; opposite letters add to 27.
• Letter and number parts may follow separate patterns.
• Squares, cubes and primes are common number patterns.
• In counting questions, check the neighbour on the correct side.
• Write the position numbers to find gaps.

Practice Questions With Answers

1. Find the next term: B, E, H, K, ?
   Answer: N
2. Find the next term: 3, 8, 15, 24, 35, ?
   Answer: 48
3. Find the next term: AB, CD, EF, GH, ?
   Answer: IJ
4. Find the next term: Z, X, V, T, ?
   Answer: R
5. Find the next term: A1, C3, E5, G7, ?
   Answer: I9
6. Find the next term: 2A, 4C, 8E, 16G, ?
   Answer: 32I
7. Find the next term: AZ, BY, CX, ?
   Answer: DW
8. Find the next term: P3, Q6, R9, S12, ?
   Answer: T15
9. Find the next term: Z, W, T, Q, ?
   Answer: N
10. Find the next term: D4, G9, J16, M25, ?
    Answer: P36

How to Practise This Chapter

Practise 10 questions every day and write the steps on paper. Then attempt timed sets from our practice papers and the previous year papers page. See all topics on the Reasoning notes page, read the previous topic Input Output Reasoning and the next topic Eligibility Test.

Frequently Asked Questions

What is an alphanumeric series?

A series made of letters and numbers (and sometimes symbols) following a pattern.

How do I solve alphanumeric series?

Convert letters to their positions and find the pattern in letters and numbers separately.

What is the opposite letter of D?

W, because 4 + 23 = 27.

What patterns are common?

Constant difference, increasing gaps, squares, cubes, doubling, and alternate series.

What is a counting question in a sequence?

A question in which you count the elements that meet a given condition in a sequence.

Is alphanumeric series asked in SSC?

Yes. It is asked in SSC CGL, CHSL and MTS reasoning.

How much time should I take?

About 30 to 40 seconds per question.

What is the position of letter M?

13.

Should I solve left to right?

Yes. Check each neighbour from left to right unless the question says otherwise.

How can I improve speed?

Learn the alphabet positions and squares, and practise daily.

What are the common mistakes?

Counting an element twice and missing the direction of preceding or following.

How do I handle symbols in the series?

Treat them as separate elements and use them only for the condition given.