Tickets for the Live 8 Africa Calling concert at the Eden Project have become available via a competition running online, by SMS and by post.
Youssou N'Dour will play London, Paris and the Eden Project
Entrants must answer the question "Where is the Eden Project?", choosing from Cornwall, London or Gleneagles.
The competition is open to all UK and Channel Island residents aged 16 and over. It closes at midnight on 24 June.
The concert, featuring a variety of African performers, will be held on 2 July, the same day as the Live 8 shows.
The line-up of Live 8 Africa Calling was announced amid criticism that the Live 8 concerts, which aim to highlight world poverty, featured too few black artists.
It will be hosted by Peter Gabriel and headlined by Senegalese star Youssou N'Dour.
Other African musicians taking part include Angelique Kidjo, Maryam Mursal, Salif Keita and Thomas Mapfumo.
Those wanting tickets can text their answer - 'A' for Cornwall, 'B' for London or 'C' for Gleneagles - to 83008 at a cost of £1.50 plus the charge of the text.
Entries can also be lodged online or by sending a postcard to the Eden Project.
When the concert line-up was announced, Peter Gabriel said it would give African artists the chance to be heard.
Kidjo said it showed that African input was needed as part of the programme of gigs around the world.
"We need to be a part of it. You couldn't help us without us," she said.
BBC Radio 3 will broadcast from the concert as part of the Live 8 coverage.
Live 8 shows have been scheduled in cities including London, Paris, Rome, Philadelphia, Tokyo and Johannesburg.
They are timed to take place days before the G8 summit of world leaders at Gleneagles, Scotland.