1+1=2 (Ichi Tasu Ichi wa Ni) is the sixth single released by Zwei and their first on Universal Music. Former WANDS member Oshima Kousuke worked with the duo once more for this single, doing the composition and arrangement for both tracks. Maeda Takahiro wrote lyrics for both songs. The title track will be used as the opening theme for the TBS program Kojin Jugyou (Private Lesson) ~Tadashii Wada Akiko no Tsukurikata~ from June to July.
Although the booklet features vocalist Ayumu without sunglasses for the first time in Zwei's history, the PV, which was filmed at Touhou Gakuen (Megu's alma mater), and made to look like a live performance, features some shots where she is wearing them. However, there are still other shots where she isn't wearing them. This is also the band's first single not released in digipak form.
- Artist: Zwei
- Title: 1+1=2 (イチ タス イチ ハ 二)
- Code: UPCH-5470
- Release Date: 2007.06.20
- Price: ￥1100
- 1+1=2 (イチ タス イチ ハ 二)
- Garakuta (がらくた; Rubbish)
- 1+1=2 (Instrumental) (イチ タス イチ ハ 二)
- Garakuta (Instrumental) (がらくた; Rubbish)