Find out the odd one in the given series:
3, 5, 8, 10, 15, 18, 24, 26
Answer & explanation
Correct answer: option 2
The correct answer is Option (2) → 18
The differences (2, 3, 2, 5, 3, 6, 2) show no single pattern, so the series is split into two series of alternate terms. Each is built on the squares 4, 9, 16, 25.
1st, 3rd, 5th and 7th terms: 3, 8, 15, 24 \(=2^2-1,\ 3^2-1,\ 4^2-1,\ 5^2-1\)
2nd, 4th, 6th and 8th terms: 5, 10, 18, 26, where the rule \(2^2+1,\ 3^2+1,\ 4^2+1,\ 5^2+1\) gives 5, 10, 17, 26
The sixth term should be 17, so 18 is the odd one out.