J.k. Rowling said this quote

You know, I don’t get why Fred and George only got three O.W.L.s each,” said Harry, watching as Fred, George, and Lee collected gold from the eager crowd. “They really know their stuff. . . .”“Oh, they only know flashy stuff that’s no real use to anyone,” said Hermione disparagingly.“No real use?” said Ron in a strained voice. “Hermione, they’ve got about twenty-six Galleons already. . . .