Number Series and Coding-Decoding: Patterns and Examples

Reasoning questions are scoring when you recognise the pattern quickly. These are the most common patterns in Bihar exams.

Number series patterns

• Constant difference: 5, 9, 13, 17, ? → add 4 → 21.
• Constant multiplier: 3, 6, 12, 24, ? → multiply by 2 → 48.
• Squares: 1, 4, 9, 16, 25, ? → 36.
• n(n+1) pattern: 2, 6, 12, 20, 30, ? → 42.
• Increasing difference: 2, 3, 5, 8, 12, ? → differences 1, 2, 3, 4, next 5 → 17.

Letter coding

• Fixed shift: if CODE is written as DPEF, each letter moves one step forward. So BIHAR becomes CJIBS.
• Reverse alphabet: A↔Z, B↔Y, C↔X. So CAT becomes XZG.
• Position values: A = 1, B = 2 … Z = 26. The word BAD = 2 + 1 + 4 = 7.

Steps to solve quickly

1. Check the difference between consecutive terms.
2. If differences are not constant, check the ratio.
3. Check squares, cubes and alternating patterns.
4. For coding, compare the first and last letters of the pair to find the rule.

Practise regularly using previous year papers and our practice sets.