i'd like to know when the band was formed
Beastie boys was  formed in 1981
awesome
They were an American hip hop group from New York City
ok, how many people were in the band
The band had Michael "Mike D" Diamond (vocals, drums), Adam "MCA" Yauch (vocals, bass) and Adam "Ad-Rock" Horovitz (vocals, guitar).
ok did everyone stay throughout the existence of the band?
No, Berry left after their first EP in 1982 and was replaced by Horovitz.