Prime Detective

How to play Prime Detective

1. Identify the prime number among composite distractors.
2. Read the prompt carefully and choose an answer, or type into the answer field.
3. After checking, read the explanation. Use “Next round” to continue.
4. Complete ten rounds for a score out of 100. Restart creates a fresh session.

A worked example

Which number is prime? Exactly two positive factors

the answer is 19. A prime is divisible only by 1 and itself.

A useful way to practice

Work out a rough answer before checking the options. If a result surprises you, use the explanation to identify the step you missed. Accuracy is more useful than rushing through a rule you have not understood.

What your result means

This is a recreational numbers activity. Results describe performance on this particular task, with this device and these rules. They are not a clinical assessment, IQ score or promise of improvements in daily life. Your best result and recent sessions stay in this browser; no account is required.