5, 11, 24, 51, 106, ? — Aptitude Question
5, 11, 24, 51, 106, ?: Find the next term: 5, 11, 24, 51, 106, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Hard
- Time target: 105 seconds
Question
Find the next term:
5, 11, 24, 51, 106, ?
Options
- 195
- 205
- 212
- 217
Show the answer and the worked solution
Correct answer: D. 217
Worked solution
- The rule is × 2 then add 1, 2, 3, 4 in turn.
- Next = 106 × 2 + 5 = 217.
Answer: 217.
The idea
When doubling leaves an inconsistent remainder, check whether that remainder itself follows a pattern.
Shortcut. The gaps 6, 13, 27, 55 each double the last and add 1, so the next gap is 111 and 106 + 111 = 217.
Common trap. 212 — doubling 106 and forgetting the growing add-on; after + 1, + 2, + 3, + 4 comes + 5, so 212 + 5.