Build the complete range, then prove it by stress-testing three carefully chosen contrast pairs.
- Enter the first and last included whole numbers.
- Use Hint for a question about half the unit, then the midpoint distance, then the inclusion rule.
- Choose In or Out for both numbers in each contrast pair.
- Use the feedback beneath each boundary or pair to repair your reasoning.
- When the range is justified, explain why the lower endpoint is included but the upper midpoint is excluded.
There is no timer, score or penalty. The aim is careful reasoning about both boundaries.
