Video: The Sing-Off Contestants Sing Part of ”Hollaback Girl” in Song Medley

This is pretty cool-during last night’s opening of the singing competition show The Sing-Off,the contestants sang a medley of The Who’s “Baba O’Reilly,” The Verve’s “Bittersweet Symphony,” Katy Perry’s “Last Friday Night (T.G.I.F.)” and “Hollaback Girl.” Check out a video below-the contestants did a really good job with the mashup!