Three of the following four numbers are alike in a certain way and one is different. Choose the number that does not belong to the group.
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 377
Check whether each number is a prime number (divisible only by 1 and itself). A number below 500 is prime if no prime up to 19 divides it, because \( 23 \times 23 = 529 \).
Option (1) 499 — 499 is not divisible by 2, 3, 5, 7, 11, 13, 17 or 19: a prime.
Option (2) 421 — 421 is not divisible by 2, 3, 5, 7, 11, 13, 17 or 19: a prime.
Option (3) 377 — \( 377 = 13 \times 29 \), so 377 is not a prime.
Option (4) 431 — 431 is not divisible by 2, 3, 5, 7, 11, 13, 17 or 19: a prime.
499, 421 and 431 are prime numbers; 377 is not, so 377 is the odd one out.