Question about duolingo
How does duolingo earn money?
We created Duolingo to give everyone free access to language education and to remove barriers from the lives of people trying to better themselves. But we're not a non-profit, and believe in making Duolingo self-sustainable so it doesn't have to rely on donations.
There are two parts to our revenue model. First, we make money by selling translations to companies like CNN and Buzzfeed. So, for example, they write their news in English, and send it to us. We then give it to our students, who in order to practice their English skills, help translate this news to their native language. Then we give the student translations back to e.g. CNN and they pay us for having translated them.
The second and most important part is our new app, the Duolingo Test Center. We’re now giving everyone the chance to prove that they have language skills without having to pay the $250 normally charged by the existing proficiency tests such as the TOEFL or the IELTS. Our tests will cost $20 (it’s free now, in Beta), and will help our educational app stay afloat.
Written by Luis Van Ahn, Co Founder
The Ceo of Duolingo explains here .. . .http://jackelliot.over-blog.com/2017/01/luis-von-ahn-an-ama-on-duolingo-subreddit.html
I hope that helps you to understand