Series - Number and Letter Series

Number and letter series are fundamental topics in reasoning sections of RRB exams. Master these patterns to score well.

Types of Series

Number Series

• Arithmetic Progression: Constant difference between terms
• Geometric Progression: Constant ratio between terms
• Mixed Series: Combination of different patterns
• Square/Cube Series: Based on perfect squares or cubes
• Prime Number Series: Based on prime numbers

Letter Series

• Alphabetical Series: Sequential or reverse alphabetical order
• Position-based Series: Based on letter positions (A=1, B=2, etc.)
• Skip Letter Series: Letters skipping fixed positions
• Mixed Letter-Number Series: Combination of letters and numbers

Quick Formulas

Number Series Patterns

• Arithmetic: a, a+d, a+2d, a+3d…
• Geometric: a, ar, ar², ar³…
• Square Series: n², (n+1)², (n+2)²…
• Cube Series: n³, (n+1)³, (n+2)³…

Letter Position Values

A=1, B=2, C=3, …, Z=26

Practice Questions

Question 1

Find the missing number: 2, 6, 12, 20, 30, ?

Question 2

Complete the series: A, C, F, J, O, ?

Question 3

Find the pattern: 1, 4, 9, 16, 25, ?

Question 4

Complete: Z, X, U, Q, L, ?

Question 5

Find missing: 3, 8, 18, 38, 78, ?

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