Mental Reasoning 1- Series: Questions and Step-by-Step Solutions for Competitive Exams SSC, BSSC, Bank, Railways

Mental Reasoning 1- Series: Questions and Step-by-Step Solutions for Competitive Exams SSC, BSSC, Bank, Railways

Mental Reasoning based on Series is one of the most common and high-scoring parts of Reasoning Ability in competitive exams like SSC, RRB, Banking, Defence, or State PSCs.

Let’s go step-by-step from the basics to advanced, covering all major types, concepts, and examples with tricks.

1. What is a Series in Mental Reasoning?

A series is a sequence of numbers, letters, or figures arranged in a specific logical order. So one has to find the pattern and predict the next/missing/wrong term.

MAIN TYPES OF SERIES QUESTIONS

There are five main types, with several subtypes:

2. NUMBER SERIES — Types & Tricks

Type 1: Simple Addition / Subtraction

• Pattern: Constant or increasing difference.

Example:
5, 8, 11, 14,?
➡ Difference = +3
Next term = 17

Type 2: Multiplication / Division

• Pattern: Multiply or divide by a constant.

Example:
2, 4, 8, 16,?
➡ Multiply by 2
Next term = 32

Type 3: Combination (Add + Multiply)

Example:
3, 6, 7, 14, 15, 30,?
➡ ×2, +1, ×2, +1 …
Next term = 31 × 2 = 62

Type 4: Square / Cube Pattern

Example:
1, 4, 9, 16, 25,?
➡ Squares (1², 2², 3², 4², 5²…)
Next = 6² = 36

Type 5: Prime / Fibonacci Series

Example (Prime): 2, 3, 5, 7, 11, 13,__? → ✅ 17
Example (Fibonacci): 1, 1, 2, 3, 5, 8, 13,__? → ✅ 21 ( Fibonacci is a sequence in which each element is the sum of the two elements that precede it .)

Type 6: Difference of Differences

Example:
3, 6, 11, 18, 27,___?
➡ 3, 5, 7, 9 → Difference increases by +2
Next difference = 11 → 27 + 11 = 38

Type 7: Alternating Pattern

Example:
2, 4, 3, 6, 4, 8, ___?
➡ +2, ×1.5 alternately
Next = 5

Type 8: Geometric / Exponential Growth

Example: 2, 4, 8, 16, 32 → multiply by 2 each time.

3. ALPHABET SERIES — Types & Tricks

         Type 1: Continuous Sequence

Example: A, C, E, G,….?
➡ +2 letters each time
Next = I

         Type 2: Reverse Alphabet Order

Example: Z, X, V, T,….?
➡ -2 each time
Next = R

         Type 3: Alternate Pattern

Example: A, Z, B, Y, C, X,….?
➡ 1st series → A, B, C…
➡ 2nd series → Z, Y, X…
Next = D, W

         Type 4: Skipping Pattern

Example: A, D, H, M,….?
➡ +3, +4, +5 …
Next = S

         Type 5: Position Code Pattern

(A=1, B=2, …, Z=26)
Example: 3, 6, 9 correspond to C, F, I

4. ALPHANUMERIC SERIES

Here, letters and numbers are combined.
You need to find a pattern in both parts.

Example:
A1, B2, C3, D4, ?
➡ Letters +1, Numbers +1
Next = E5

Example:
A2, C4, E6, G8, ?
➡ Letters +2, Numbers +2
Next = I10

Example:
1A, 2B, 4C, 8D, ?
➡ Numbers ×2, Letters +1
Next = 16E

5. MIXED SERIES (With Symbols)

Example:
A1$, B2%, C3&, D4#, ?
➡ Letters +1, Numbers +1, Symbols fixed pattern
Next = E5@

Example:
Z9#, X8$, V7%, ?
➡ Letters -2, Numbers -1
Next = T6^

6. LOGICAL / FIGURATIVE SERIES

These are non-verbal reasoning types — appear in SSC, RRB, NDA, etc.

🔸 Type 1: Shape Change

Square → Pentagon → Hexagon → ?
Heptagon

🔸 Type 2: Rotation / Flip

Arrow pointing ↑ → → ↓ → ?
Next = ←

🔸 Type 3: Shading / Counting Parts

Patterns alternate in shading, dot positions, or line counts.

7. Special & Trick Series

8. Shortcut Strategy

Observe the difference/ratio
Check alternate terms
See if it involves squares/cubes/primes
Watch for repetition or interleaving
Convert letters → positions (A=1…Z=26)
Look for increasing, decreasing, or reverse patterns

9. Common Question Types in Exams

10. PRACTICE EXAMPLES (With Solutions)

Q1: 1, 2, 6, 24, 120,?

→ Multiply by 1, 2, 3, 4, 5 → ✅ Next = 720

Q2: 2, 6, 12, 20, 30,?

→ Difference: +4, +6, +8, +10 → ✅ Next = 42

Q3: A, D, I, P, ?

→ +3, +5, +7 → ✅ Next = Y

Q4: B1, D4, F9, H16, ?

→ Letters +2, Numbers are squares (1, 4, 9, 16) → ✅ Next = J25

Q5: 5, 10, 20, 40, ?, 160

→ ×2 pattern → ✅ Missing = 80

11. Practice Tip

• Easy to Hard order: Number → Alphabet → Alphanumeric → Mixed → Figural
• Time-saving trick: If the difference keeps changing → write 2nd difference
• Practice 10–15 questions per type daily.