Find the odd one out: 1, 4, 9, 15, 25.

15

1, 4, 9, and 25 are perfect squares (1², 2², 3², 5²), but 15 is not a perfect square.

Understanding Reasoning questions

Reasoning questions test pattern recognition rather than subject knowledge. They are solved by testing one hypothesis at a time against every element in the question.

How to approach it

1. Look for the relationship between the first two elements.
2. Test that relationship on the remaining elements.
3. If it fails, look for an alternating or two-step pattern.
4. Confirm the chosen answer fits every element, not just the closest one.

Common mistakes to avoid

• Settling on the first pattern that fits only part of the series.
• Missing an alternating pattern in a mixed sequence.
• Bringing outside assumptions into a purely logical question.

Where it appears: Standard in school aptitude tests, olympiads and competitive entrance exams.