The odd one out among primes — Aptitude Question
The odd one out among primes: Which number does not belong? 17, 23, 29, 33, 41 Answer and worked solution on CodeKairo.
- Topic: Number & Letter Series
- Section: Logical Reasoning
- Difficulty: Easy
- Time target: 40 seconds
Question
Which number does not belong?
17, 23, 29, 33, 41
Options
- 17
- 23
- 33
- 41
Show the answer and the worked solution
Correct answer: C. 33
Worked solution
- 17, 23, 29 and 41 are prime.
- 33 = 3 × 11 is composite.
Answer: 33.
The idea
Check divisibility by 3 and 7 quickly — those catch most of the composite traps in this range.
Shortcut. 33 has digit sum 6, so it is divisible by 3 (33 = 3 × 11); the other numbers pass that test and are prime.
Common trap. 41 — the jump from 33 to 41 is 8 while the earlier gaps are 6, so it looks out of rhythm; but the test is primality, and 41 is prime.