Find the odd one out:
Answer & explanation
Correct answer: option 4
The correct answer is Option (4) → 93
Option (1) 23 — a prime number: its only factors are 1 and 23.
Option (2) 43 — a prime number: its only factors are 1 and 43.
Option (3) 73 — a prime number: its only factors are 1 and 73.
Option (4) 93 — \(93=3\times31\), so 93 is the odd one out, the only number that is not prime.
Tip: A number is divisible by 3 when the sum of its digits is: \(9+3=12\), so 93 has the factor 3, while 23, 43 and 73 (digit sums 5, 7, 10) do not.