336, 210, 120, 60, 24, ? — Aptitude Question
336, 210, 120, 60, 24, ?: Find the next term: 336, 210, 120, 60, 24, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Hard
- Time target: 105 seconds
Question
Find the next term:
336, 210, 120, 60, 24, ?
Options
- 6
- 8
- 10
- 12
Show the answer and the worked solution
Correct answer: A. 6
Worked solution
- 7³ − 7 = 336, 6³ − 6 = 210, 5³ − 5 = 120, 4³ − 4 = 60, 3³ − 3 = 24.
- Next is 2³ − 2 = 6.
Answer: 6.
The idea
A rapidly falling series usually runs on a decreasing n. Test n³ − n and n³ + n against the largest term first.
Shortcut. Read each term as three consecutive numbers multiplied: 6 × 7 × 8, 5 × 6 × 7, 4 × 5 × 6, 3 × 4 × 5, 2 × 3 × 4 — so the next is 1 × 2 × 3 = 6.
Common trap. 12 — noticing that 120 halves to 60 and halving 24 as well; 60 → 24 is not a halving, so that rule never held.