The rock band joined by Tru Collins in 2010 has sold approx. how many concert tickets?
Tru Collins:  In 2010, she joined Atlantic Records' multi-platinum progressive rock band Trans-Siberian Orchestra as a vocalist, touring arenas across North America and promoting the band performing acoustic guitar/vocal solos live on numerous rock radio stations. Trans-Siberian Orchestra:  TSO has sold more than 10 million concert tickets and over 10 million albums.
10 million