Quizlet is now the ~50th biggest website in the U.S.
Not to say 150th isn't impressive or likely a lot of traffic.. but if you're going to post a number and claim like that, it should be accurate.
Ballpark, I'd say that's between 700 and 1,000 hits/second on the main frontend. I sort of doubt either AWS or GCP is so much faster than the other for this kind of load.
Quantcast is usually more accurate and Quizlet US Rank on Quantcast is 37.
http://imgur.com/TcuxQ6t
Not to say 150th isn't impressive or likely a lot of traffic.. but if you're going to post a number and claim like that, it should be accurate.