Has this happened to you? You are on your Standards Progress Report page and you click a link like the ones circled in red above to review something or level up. The link takes you to the Khan Academy app on your iPad, but instead of the expected location, you end up on the home page or with a request to log in again. What happened?
It's not you, it's your device. For some reason, the Khan Academy app on iOS doesn't always read standard web addresses (URL's) correctly. In the case of the link labeled "KA Unit Rates - MasterY" in the image above, the URL the link wants to take you is
Translation: Khan Academy, then Math, then Common Core (cc) 6th Grade Math - not much help. Next is cc-6th-ratios-prop-topic - a-ha! now we're getting somewhere.
In the iPad app, find 6th Grade Math in Courses and look for a Topic with Ratios in the title. The URL ends with Quiz 3 - see if there is a quiz 3 in that topic.
Congratulations, you've found it. Sorry I can't help with the mastery part, but you've got it.
I will try to figure out an easier way to access materials without the detective work...