http://www.billboard.com/articles/events/greatest-of-all-time/6760662/beatles-mariah-carey-most-billboard-hot-100-no-1-hits
The list of acts with the most Hot 100 No. 1s was compiled from the chart's Aug. 4, 1958 inception through the chart dated Oct. 10, 2015.
The first sentence beneath the title of the quiz contains two of the answers to this quiz. It helped me a little, as I scored 6/9. Thanks for the quiz!
Of course you would start from 1958, when the Hot 100 started, and not from when Elvis hit the #1 spot in early 1956 with Heartbreak Hotel. Elvis had 18 #1 hits, second only to the Beatles!!! Prior to the Billboard Hot 100, the songs that made # 1 counted. For those of you out there that do not know, Rock Around The Clock by Bill Haley and His Comets, was the first Rock and Roll song to ever become a #1 national hit record.