Who sang background on the song En karusell when they were just 27 years old?
En karusell:  Future members of ABBA Agnetha Fältskog and Anni-Frid Lyngstad did backing vocals on the song but were not credited for their contribution.The B-side song on the Swedish release was titled "Att finnas till" and the B-side song on the Japanese release was titled "Lycka". Anni-Frid Lyngstad: Anni-Frid Synni, Princess Reuss of Plauen (German: "Anni-Frid Synni, Prinzessin Reuß von Plauen" ; born Anni-Frid Synni Lyngstad, 15 November 1945), commonly known as Frida Lyngstad, or just by the mononym, Frida, is a Norwegian-born Swedish singer, songwriter, and environmentalist.
Anni-Frid Lyngstad