Number Series Tricks
π’ Number Series β 60-Second Revision
| Type | Signature | Quick Check | Example | Missing Term |
|---|---|---|---|---|
| Arithmetic | Constant diff | Ξ = same | 3, 7, 11, 15β¦ | 19 |
| Geometric | Constant ratio | Γ· = same | 5, 10, 20, 40β¦ | 80 |
| Prime | Only Γ·1 & itself | 2-3-5-7-11β¦ | 4, 9, 25, 49β¦ | 121 (11Β²) |
| Square | nΒ² | Last digit 0,1,4,5,6,9 | 1, 4, 9, 16β¦ | 25 |
| Cube | nΒ³ | Last digit same as base | 1, 8, 27, 64β¦ | 125 |
| Fibonacci | Tβ=Tβββ+Tβββ | 1,1,2,3,5β¦ | 2, 3, 5, 8β¦ | 13 |
| Alternating | Two AP/GP mixed | Odd-even split | 2, 5, 4, 7, 6β¦ | 9 |
| Digit-op | Sum/product of digits | 18β1Γ8=8, 27β2Γ7=14 | 12, 24, 36β¦ | 48 |
π§ Mnemonics
- AP: βAdd-Pβ (Add Plus) β same difference
- GP: βGo-Productβ β same multiply
- Prime: β2-3-5-7-11β β count on fingers
- Squares 1-20: β1-4-9-16-25-36-49-64-81-100-121-144-169-196-225-256-289-324-361-400β (rhyme in 5-sec)
- Cubes 1-10: β1-8-27-64-125-216-343-512-729-1000β β say β1-8-27β like a phone number
β‘ Rapid-Fire MCQs
Question 1: 4, 9, 16, 25, ?
Answer: 36Question 2: 5, 10, 20, 40, ?
Answer: 80Question 3: 3, 5, 9, 17, 33, ?
Answer: 65Question 4: 2, 5, 10, 17, 26, ?
Answer: 37Question 5: 1, 1, 2, 3, 5, 8, ?
Answer: 13Question 6: 121, 112, 103, 94, ?
Answer: 85Question 7: 8, 27, 64, 125, ?
Answer: 216Question 8: 7, 14, 17, 34, 37, ?
Answer: 74Question 9: 18, 27, 36, 45, ?
Answer: 54Question 10: 2, 3, 5, 7, 11, ?
Answer: 13π― Exam Hack
- Spot last digit first β eliminates 3 options in 3s.
- If diff/ratio fails in 2 steps β switch to alternate or digit pattern.
- 90% railway series use AP, GP, Square, Prime β attempt these first.
BETA
