Duolingo tapped AI and machine learning to create a cheaper, faster English proficiency test that the company claims is on par with proctored exams.

The test will cost $20, as compared to $300 for equivalent in-person certification tests. Duolingo plans to launch the service in three weeks.

Hundreds of millions of people worldwide own smartphones, and many of them are learning English. Duolingo sees a moneymaking opportunity.