Conversation so far:
who is inducted in the rock hall of fame
2020 inductees into the Rock & Roll Hall of Fame include Depeche Mode, The Doobie Brothers, Whitney Houston, Nine Inch Nails, The Notorious B.I.G., and T. Rex.
when do tickets go on sale for the rock and roll hall of fame induction
Tickets for the 2020 Rock and Roll Hall of Fame induction ceremony went on sale to the general public through TicketMaster at 10 a.m. Thursday, Feb. 27.
when will the 2020 rock and roll exhibit go up
The Rock & Roll Hall of Fame Class of 2020 special exhibit will go on display in the museum at the end of April 2020.

Question: how many ceremonies have there been
Self-contained rewrite: how many rock and roll hall of fame induction ceremonies have there been