ReasoningAbility.com

Alternating Series

Alternating Series problems involve sequences where two different patterns interleave. For example, odd positions follow one progression while even positions follow another. These problems test your ability to separate interleaved patterns and analyze them independently.

10Worksheets
200+Practice Questions
IntermediateDifficulty
2-3 hoursHours to Master

What You'll Learn

Introduction & Overview Why This Matters How to Solve Pro Tips & Tricks
Shortcut Methods Common Mistakes Practice Worksheets Exam Importance

Introduction to Alternating Series

Alternating Series problems involve sequences where two different patterns interleave. For example, odd positions follow one progression while even positions follow another. These problems test your ability to separate interleaved patterns and analyze them independently.

Prerequisites

Alphabet position knowledge Understanding of pattern separation Arithmetic progression concepts Position parity (odd/even) identification
Why This Matters: Alternating Series problems appear in 1-2 questions in SSC CGL and Banking PO exams. They test pattern separation and dual-sequence analysis.

How to Solve Alternating Series Problems

1

Step 1: Separate odd-position terms (1st, 3rd, 5th...) into one sequence

2

Step 2: Separate even-position terms (2nd, 4th, 6th...) into another sequence

3

Step 3: Analyze each subsequence independently for its pattern

4

Step 4: Determine which position the next term occupies

5

Step 5: Apply the appropriate pattern to find the next term

6

Step 6: Convert position back to letter if needed

7

Step 7: Verify both patterns are consistent

Pro Strategy: Write the sequence with position numbers. Separate odd and even positions into two lists. Find the pattern in each list independently. The next term's pattern is determined by its position parity.

Example Problem

Example: Find the next letter: A, C, B, D, C, E, D, ___ Solution: Step 1: Odd positions (1st,3rd,5th,7th): A, B, C, D → +1 each Step 2: Even positions (2nd,4th,6th): C, D, E → +1 each Step 3: Next is 8th term (even position) Step 4: Next even term = E + 1 = F Answer: F

Pro Tips & Tricks

  • Odd positions (1st, 3rd, 5th, 7th...) form one sequence
  • Even positions (2nd, 4th, 6th, 8th...) form another sequence
  • Each subsequence usually follows a simple pattern (consecutive, skip, etc.)
  • The step size may be different for each subsequence
  • Some alternating patterns have three or more interleaved sequences
  • Always check position parity before applying the pattern

Shortcut Methods to Solve Faster

If odd positions increase by +1, even positions also increase by +1, the pattern is two interleaved arithmetic progressions
For alternating +1, +2: odd positions +1, even positions +2
The next term's pattern is determined by whether its position is odd or even

Common Mistakes to Avoid

Trying to find a single pattern for the entire sequence
Misidentifying which terms belong to which subsequence
Not checking both subsequences for consistency
Forgetting to determine the parity of the next term's position

Exam Importance

Alternating Series is an important topic for various competitive exams. Here's how frequently it appears:

SSC CGL
1-2 questions
BANKING PO
1-2 questions
RAILWAYS RRB
1-2 questions
INSURANCE
1-2 questions

Ready to Master Alternating Series?

Start with Worksheet 1 and work your way up to expert level! Each worksheet includes:

20 practice questions
Detailed solutions
Step-by-step explanations
Start Practicing Now