5, 10, 20, 40, ? — Number & Letter Series Aptitude Question
5, 10, 20, 40, ?: Find the next term: 5, 10, 20, 40, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 30 seconds
Question
Find the next term:
5, 10, 20, 40, ?
Options
- 50
- 60
- 80
- 100
Show the answer and the worked solution
Correct answer: C. 80
Worked solution
- The ratio is 2 throughout.
- Next = 40 × 2 = 80.
Answer: 80.
The idea
Check the ratio between consecutive terms first when the series grows quickly but smoothly.
Shortcut. The terms are 5 × 1, 5 × 2, 5 × 4, 5 × 8, so the next is 5 × 16 = 80.
Common trap. 60 — adding the last gap, 20, again (40 + 20); in a doubling series the gaps double too, so the next gap is 40.