20, 19, 17, 14, 10, ? — Aptitude Question
20, 19, 17, 14, 10, ?: Find the next term: 20, 19, 17, 14, 10, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 40 seconds
Question
Find the next term:
20, 19, 17, 14, 10, ?
Options
- 3
- 4
- 5
- 6
Show the answer and the worked solution
Correct answer: C. 5
Worked solution
- Differences: −1, −2, −3, −4.
- Next = 10 − 5 = 5.
Answer: 5.
The idea
Falling by one more each time. Write the differences out rather than trying to see the rule in the terms.
Shortcut. Term n is 20 minus a triangular number (0, 1, 3, 6, 10), so the sixth is 20 − 15 = 5.
Common trap. 6 — subtracting 4 again (10 − 4); each drop is one bigger than the last, so the next is 5.