2, 5, 11, 23, 47, ? — Aptitude Question
2, 5, 11, 23, 47, ?: Find the next term: 2, 5, 11, 23, 47, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 45 seconds
Question
Find the next term:
2, 5, 11, 23, 47, ?
Options
- 83
- 91
- 95
- 96
Show the answer and the worked solution
Correct answer: C. 95
Worked solution
- 2×2+1 = 5, 5×2+1 = 11, 11×2+1 = 23, 23×2+1 = 47.
- Next = 47 × 2 + 1 = 95.
Answer: 95.
The idea
Once the doubling rule is confirmed on three consecutive pairs, apply it once more. No need to find a closed form.
Shortcut. Add 1 to every term: 3, 6, 12, 24, 48 doubles cleanly, so the blank is 96 − 1 = 95. After the first, every term is odd, so 96 is out.
Common trap. 96 — the next term of the shifted series 3, 6, 12, 24, 48, i.e. forgetting to take back the 1 added (47 × 2 + 2 is the same slip).