7, 10, 8, 11, 9, ? — Aptitude Question
7, 10, 8, 11, 9, ?: Find the next term: 7, 10, 8, 11, 9, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 45 seconds
Question
Find the next term:
7, 10, 8, 11, 9, ?
Options
- 6
- 10
- 12
- 13
Show the answer and the worked solution
Correct answer: C. 12
Worked solution
- 7 + 3 = 10; 10 − 2 = 8; 8 + 3 = 11; 11 − 2 = 9.
- Next = 9 + 3 = 12.
Answer: 12.
The idea
A zig-zag series alternates a rise and a fall. Read the differences in order: +3, −2, +3, −2.
Shortcut. The even-position terms 10, 11, ? rise by 1, so the sixth term is 12 — each + 3, − 2 pair nets + 1.
Common trap. 10 — adding the net + 1 to the last term 9; the + 1 links terms two apart, and the step due now is + 3.