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.