Avril Lavigne: 90 million, let's say 80 (as Billboard says) in case you don't like. 

I calculated ALL the sales of Avril Lavigne as listed with SOURCES in her wikipedia album pages. And... Billboard says 30 hell yeah but nikkansports says 40 million. Because: Let Go 20m + Under My Skin 12m, The Best Damn Thing 8m, Goodbye Lullaby 2m + Avril Lavigne 650,000 = 42,650,000 (Which all of them are sourced in her discography page. Which makes it 90m. Claimed 40m albums + 50m singles = 90m. What is wrong with wikipedia by the way? Drat! All pages says different things even if they have a SOURCE. People hint undo pitilessly. I'm not saying you or everyone do that way but "please" check her pages.