Letter-Number-Symbol Series: Counting by Neighbours and Finding Positions
Letter-Number-Symbol Series: Counting by Neighbours and Finding Positions
These questions give a long mixed series of letters, digits and symbols and ask you to count elements that meet a condition about their neighbours, or to find the element at a position after the series is changed. They need no formula, only a careful, systematic scan. Mark each candidate in one pass and check its neighbours; never count from memory.
1. Method Box
| Task | Method |
|---|---|
| Count X immediately preceded by Y and followed by Z | Scan for every X, then check the element just before and just after it |
| "Not preceded by" clauses | First list the matches, then strike out those with the forbidden neighbour |
| k-th to the left of the m-th from the right | Convert to a position from the left: (n − m + 1) − k, where n is the length |
| After reversing the series | The m-th from the right of the reversed series is the m-th from the left of the original; left and right swap |
| After removing all symbols (or digits) | Rewrite the shortened series before counting positions |
Number every element of the series once (1, 2, 3 ...) and work with positions
Odd digits: 1, 3, 5, 7, 9. Even digits: 0, 2, 4, 6, 8. Vowels: A, E, I, O, U
✗ Counting the last element as "followed by" something | ✓ The last element has no follower; it can never meet a "followed by" condition
✗ After reversing, "to the left" means the same direction as before | ✓ In the reversed series, moving left equals moving right in the original
हिंदी नोट: मिश्रित श्रेणी में हर तत्व को क्रमांक दीजिए और एक-एक करके पड़ोसी जाँचिए। श्रेणी उलटने पर बायाँ और दायाँ आपस में बदल जाते हैं। चिह्न हटाने के बाद नई श्रेणी दोबारा लिखिए।
Exam Pointer: Verified NTPC patterns: counting by neighbours in mixed and number-symbol series (August 2025 UG CBT-1, June 2025 Graduate CBT-1, June 2022 CBT-2), positions after reversing (May 2022 CBT-2), digit-only series with odd and even neighbours (June 2026 UG CBT-1, August 2025 UG CBT-1) and positions after removing symbols (March 2026 Graduate CBT-1). Plain property counts had no separate verified shift and are tagged syllabus-based.
2. Series for Patterns 1, 2, 3 and 5
Series A (23 elements): R 4 % M 7 @ 2 K # 9 E 5 ★ T 3 ▲ 8 B * 1 W 6 ©
| Position | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 | 11 | 12 |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Element | R | 4 | % | M | 7 | @ | 2 | K | # | 9 | E | 5 |
| Position | 13 | 14 | 15 | 16 | 17 | 18 | 19 | 20 | 21 | 22 | 23 |
|---|---|---|---|---|---|---|---|---|---|---|---|
| Element | ★ | T | 3 | ▲ | 8 | B | * | 1 | W | 6 | © |
Pariksha Pattern: Every Way NTPC Asks This Topic
Pattern 1: Counting elements by their neighbours
[PYQ: NTPC UG CBT-1 18-Aug-2025 Shift-3 | NTPC CBT-2 13-Jun-2022 Shift-1 | NTPC Graduate CBT-1 18-Jun-2025 Shift-2]
EXAM LEVEL
Q. In Series A, how many numbers are immediately preceded by a symbol and immediately followed by a letter?
Check each number: @ 2 K, # 9 E, ▲ 8 B and * 1 W fit. 4, 7, 5, 3 and 6 fail (for example, 4 is preceded by R).
Answer: 4
EXAMATLAS LEVEL
Q. In Series A, how many symbols are immediately preceded by a number and immediately followed by a letter? How many letters are immediately preceded by a number and followed by a symbol?
Symbols: 4 % M and 5 ★ T fit; 7 @ 2 and 3 ▲ 8 are followed by numbers, and © is last. Letters: 2 K # and 8 B * fit.
Answer: 2 symbols; 2 letters
Pattern 2: Positions from either end, and after reversing
[PYQ: NTPC CBT-2 10-May-2022 Shift-1]
EXAM LEVEL
Q. In Series A, which element is 5th to the left of the 9th element from the right end?
The 9th from the right is position 23 − 9 + 1 = 15 (the digit 3). Five to its left is position 10: 9.
Answer: 9
EXAMATLAS LEVEL
Q. If Series A is written in reverse order, which element will be 4th to the left of the 8th element from the right end?
The 8th from the right of the reversed series is the 8th from the left of the original: K (position 8). In the reversed series, moving left means moving right in the original: position 8 + 4 = 12, which is 5.
Answer: 5
Pattern 3: Digit-only series with odd and even neighbours
[PYQ: NTPC UG CBT-1 20-Jun-2026 Shift-2 | NTPC UG CBT-1 11-Aug-2025 Shift-3]
Series B: 5 7 2 9 4 8 3 1 6 7 5 3 2 8 4 9 1 7
EXAM LEVEL
Q. In Series B, how many even digits are immediately preceded by an odd digit and immediately followed by an even digit?
9 4 8 (positions 4 to 6) and 3 2 8 (positions 12 to 14) fit. The other even digits fail: 2 is followed by 9, the 8 at position 6 is preceded by 4, 6 is followed by 7, the 8 at position 14 is preceded by 2, and the 4 at position 15 is followed by 9.
Answer: 2
EXAMATLAS LEVEL
Q. In Series B, how many odd digits are immediately preceded by an even digit and immediately followed by an even digit? And how many 5s are immediately followed by 3 but not immediately preceded by 7?
Only 2 9 4 fits the first condition. The only 5 followed by 3 is at position 11, and it is preceded by 7 (position 10), so it is struck out.
Answer: 1; 0
Pattern 4: Positions after removing symbols
[PYQ: NTPC Graduate CBT-1 27-Mar-2026 Shift-1]
EXAM LEVEL
Q. If all symbols are removed from Series A, how many elements remain?
Series A has 7 symbols (%, @, #, ★, ▲, *, ©), so 23 − 7 = 16 remain.
Answer: 16
EXAMATLAS LEVEL
Q. If all symbols are removed from Series A, which element is 6th from the left and which is 4th from the right?
The new series is R 4 M 7 2 K 9 E 5 T 3 8 B 1 W 6. The 6th from the left is K. With 16 elements, 4th from the right is position 13: B.
Answer: K; B
Pattern 5: Plain property counts
[Pattern: syllabus-based, PYQ-style]
EXAM LEVEL
Q. How many odd digits are there in Series A?
The digits are 4, 7, 2, 9, 5, 3, 8, 1, 6; the odd ones are 7, 9, 5, 3 and 1.
Answer: 5
EXAMATLAS LEVEL
Q. In Series A, how many vowels are there, and how many letters are immediately followed by a digit?
The letters are R, M, K, E, T, B, W, and only E is a vowel. Letters followed by a digit: R 4, M 7, E 5, T 3 and W 6, which is 5.
Answer: 1 vowel; 5 letters
60-Second Revision
- Number the series first and work by positions.
- Check both neighbours of every candidate; the first and last elements have only one neighbour.
- Reversed series: left and right swap.
- Rewrite the series after removing elements.
Next Step: Letter-Number-Symbol series done. Practise one such series a day in the ExamAtlas RRB NTPC 2026 mock tests; number the elements before reading the question.