In this guide
An alphanumeric series is a row of mixed letters, numbers and symbols, usually 20 to 30 elements long, followed by a set of questions. Nothing in it needs a clever idea. Every question is a counting task, and every wrong answer is a counting slip.
That makes it a good set to attempt once you have a steady hand, and a bad one to rush. One careful count takes less time than two hurried ones and a guess. This guide gives you the position formulas, a safe way to count, and two full sets to practise on.
The question types
| Type | Example wording |
|---|---|
| Position | Which element is 5th from the right end? |
| Relative position | Which element is 4th to the right of the 8th from the left? |
| Neighbour pairs | How many letters are immediately followed by a number? |
| Neighbour triples | How many numbers are immediately preceded by a letter and immediately followed by a symbol? |
| Removal | If all the symbols are removed, which element is 6th from the left? |
| Rearrangement | If the first nine elements are written in reverse order, which element is 7th from the left? |
| Counting a kind | How many even numbers are there in the series? |
The position formulas
Number the positions from the left, 1 to n. Then every instruction becomes one small sum.
| Instruction | Position from the left |
|---|---|
| kth from the left | k |
| kth from the right | n + 1 − k |
| m to the right of the kth from the left | k + m |
| m to the left of the kth from the left | k − m |
| m to the left of the kth from the right | n + 1 − k − m |
| m to the right of the kth from the right | n + 1 − k + m |
A safe counting method
- Number the series lightly under it, or mark every fifth element. Counting in fives halves the errors.
- Convert everything to "from the left" with the formulas before you look up an element.
- For neighbour questions, sweep once from left to right. Look at each element and its neighbour, and tick the pairs that match. Do not jump around.
- For removal and rearrangement questions, write the new short series out before counting. It takes ten seconds and saves most errors.
- Recount any answer that depends on more than ten steps.
A fully worked set
Series: K 4 @ M 7 B % 2 D 9 # E 5 $ R 3 & T
| 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 | 13 | 14 | 15 | 16 | 17 | 18 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| K | 4 | @ | M | 7 | B | % | 2 | D | 9 | # | E | 5 | $ | R | 3 | & | T |
The series has 18 elements: 7 letters, 6 numbers and 5 symbols.
Q1. How many letters are immediately followed by a number?
- Sweep the pairs: K4, M7, D9, E5, R3 match. B is followed by %, and T is the last element.
- Five.
Q2. How many symbols are immediately preceded by a number?
- 4@, 9#, 5$, 3& match. % is preceded by B.
- Four.
Q3. Which element is 5th from the right end?
- 18 + 1 − 5 = 14th from the left.
- $.
Q4. Which element is 4th to the right of the 8th element from the left?
- 8 + 4 = 12th from the left.
- E.
Q5. If all the symbols are removed, which element is 6th from the left?
- New series: K 4 M 7 B 2 D 9 E 5 R 3 T.
- 2.
Q6. Which element is 3rd to the left of the 6th element from the right?
- 18 + 1 − 6 − 3 = 10th from the left.
- 9.
Q7. If the first nine elements are written in reverse order, which element is 7th from the left?
- The first nine are K 4 @ M 7 B % 2 D. Reversed: D 2 % B 7 M @ 4 K.
- The 7th of these is @.
Common mistakes
- Mixing up "immediately preceded by" and "immediately followed by". Say the pair in the order the question states it, for example "letter, then number".
- Counting the reference element itself when moving "4 to the right". Start from the next element.
- Forgetting that a number like 9 is one element, and a symbol like % is one element.
- In removal questions, counting on the original series out of habit.
- In triple questions ("preceded by a letter and followed by a symbol"), checking only one side.
Practice set
Series: 7 R # 3 A B % 8 Q 5 @ W 2 N $ 6 H 9 & L 4
Number the positions yourself first. Aim for five minutes.
- How many numbers are immediately followed by a letter?
- How many symbols are immediately preceded by a letter and immediately followed by a number?
- Which element is 7th from the right end?
- Which element is 5th to the left of the 14th element from the left?
- If all the numbers are removed, which element is 8th from the left?
- How many letters are there in the series?
- If the first ten elements are written in reverse order, which element is 4th from the left?
- How many odd numbers are immediately preceded by a symbol?
Answers:
- Five. 7R, 3A, 8Q, 2N and 6H. (5 is followed by @, 9 by &, and 4 is last.)
- Three. R # 3, B % 8 and N $ 6. The @ and & are preceded by numbers.
- $. The series has 21 elements. 21 + 1 − 7 = 15th from the left.
- Q. 14 − 5 = 9th from the left.
- W. Without numbers: R # A B % Q @ W N $ H & L. The 8th is W.
- Eight. R, A, B, Q, W, N, H and L.
- %. The new 4th is the old (10 + 1 − 4) = 7th element, which is %.
- One. Only #3. The other odd numbers (7, 5, 9) are first in the series or come after a letter.
What to do next
- Write the six position formulas from memory before each practice session this week.
- Do one full series set a day, timed, and recount every answer that took more than ten steps.
- Keep a tally of which question type you got wrong. Most people have one weak type, usually triples or reverse questions.
- Next, practise alphabet-based questions and coding–decoding, which use the same careful counting.
A note on dates and numbers. Exam patterns, vacancies and schedules change from year to year. Always confirm the current details in the latest notification on the Institute of Banking Personnel Selection website .
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