Example 1
Find the next number: 20, 24, 29, 35, 42, 50, ?
Answer: A) 59
Differences are 4, 5, 6, 7, 8, growing by 1; next difference 9, so 50 + 9 = 59.
Number Series reasoning questions for competitive exams: rules, worked examples and practice
Number series questions ask for the next term (or a wrong term) of a pattern. Start with the differences between terms.
Key rules and formulas
- Check first differences, then second differences.
- Look for multiplication (×2, ×3) or a mix (×2 + 1).
- Squares, cubes and primes are common bases.
- Two series can alternate in odd and even positions.
Common traps
- Stopping at the first pattern that fits two terms; check all of them.
- Missing an alternating series.
Where Number Series is asked
- IBPS Clerk Prelims (Reasoning Ability)
- IBPS PO Prelims (Reasoning Ability)
- RRB Group D (General Intelligence & Reasoning, Reasoning)
- RRB NTPC CBT 1 (General Intelligence & Reasoning, Reasoning)
- SBI Clerk Prelims (Reasoning Ability)
- SBI PO Prelims (Reasoning Ability)
- SSC CGL Tier 1 (General Intelligence & Reasoning, Reasoning)
- SSC CGL Tier 2 (General Intelligence, Reasoning & General Intelligence)
- SSC CHSL Tier 1 (General Intelligence)
Worked examples
Example 2
Find the next term: 17, 26, 37, 50, 65, ?
Answer: C) 82
Terms are n² + 1 for n = 4…8; next is 9² + 1 = 82.
Example 3
Find the next number in the series: 13, 25, 37, 49, 61, ?
Answer: D) 73
Each term increases by 12: 61 + 12 = 73.
More Number Series practice questions
- Find the next term: 80, 99, 120, 143, 168, ?
- Find the next number in the series: 6, 17, 28, 39, 50, ?
- Which number comes next? 8, 28, 88, 268, 808, ?
- Find the next number in the series: 39, 46, 53, 60, 67, ?
- Which number comes next? 9, 31, 97, 295, 889, ?
- Which number comes next? 2, 5, 11, 23, 47, ?
- Find the next number: 3, 7, 14, 24, 37, 53, ?
- Find the next number: 12, 13, 18, 27, 40, 57, ?
- Find the next term: 5, 10, 17, 26, 37, ?
- Which number completes the series: 3, 7, 15, 31, ?
Frequently asked questions
What is Number Series in competitive exams?
Number series questions ask for the next term (or a wrong term) of a pattern. Start with the differences between terms.
Which exams ask Number Series questions?
On MockBazaar, Number Series questions appear in IBPS Clerk Prelims, IBPS PO Prelims, RRB Group D, RRB NTPC CBT 1, SBI Clerk Prelims, SBI PO Prelims, SSC CGL Tier 1, SSC CGL Tier 2, SSC CHSL Tier 1.
What is the most common mistake in Number Series?
Stopping at the first pattern that fits two terms; check all of them.