16 of the biggest hits of the year in piano/vocal/guitar arrangements, including: All of Me (John Legend) • Best Day of My Life (American Authors) • Dark Horse (Katy Perry) • Fancy (Iggy Azalea) • Happy (Pharrell Williams) • Let It Go (Idina Menzel) • Pompeii (Bastille) • Problem (Ariana Grande) • Raging Fire (Phillip Phillips) • Timber (Pitbull featuring Ke$ha) • and more.