3, 8, 15, 24, 35, ? — Aptitude Question
3, 8, 15, 24, 35, ?: Find the next term: 3, 8, 15, 24, 35, ? Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 45 seconds
Question
Find the next term:
3, 8, 15, 24, 35, ?
Options
- 42
- 45
- 48
- 50
Show the answer and the worked solution
Correct answer: C. 48
Worked solution
- The terms are 2² − 1, 3² − 1, 4² − 1, 5² − 1, 6² − 1.
- Next = 7² − 1 = 48.
Answer: 48.
The idea
Add one to each term and see whether the results are recognisable. Small offsets from squares and cubes are extremely common.
Shortcut. Each term is a product of two numbers two apart: 1 × 3, 2 × 4, 3 × 5, 4 × 6, 5 × 7, so the next is 6 × 8 = 48.
Common trap. 50 — flipping the offset to 7² + 1; the terms sit one below the squares (4 − 1, 9 − 1, …), not one above, so the answer is 49 − 1.