1-1 is a mathematical expression that evaluates to:
- 0 (number) (in ordinary arithmetic)
The term 1-1 may refer to:
- New Year's Day, a public holiday in many countries, held annually on the first of January
- Schweizer SGP 1-1, an American glider design
- World 1-1, the first level of Nintendo's Super Mario Bros.
See also
- 1:1 (disambiguation)
- 1+1 (disambiguation)
- One-to-one (disambiguation)
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