Which number is not like the others in the series?
3, 5, 20, 23, 37
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 20
A prime number has only two factors, 1 and itself. In the series 3, 5, 20, 23, 37, every number except one is prime.
Option (1) 5 — Incorrect. A prime number: its only factors are 1 and 5.
Option (2) 20 — Correct. \(20=2\times2\times5\), so it is not prime (it is also the only even number), so 20 is the odd one out.
Option (3) 37 — Incorrect. A prime number: no number from 2 to 6 divides it.
Option (4) 23 — Incorrect. A prime number: its only factors are 1 and 23.