Photomath just raised a $6 million funding round from Goodwater Capital, with Learn Capital also participating. Photomath has created a hugely successful mobile app for iOS and Android with 100 million downloads so far.

Photomath first launched at TechCrunch Disrupt London back in 2014. The company was working on text recognition technology. Photomath was just a demo app to promote that technology.

But the startup accidentally created a consumer success. The app instantly attracted millions of downloads from many desperate students willing to learn math with their phones.

Years later it is still one of the most downloaded apps in the App Store and Play Store. And the reason it’s been so successful is that it’s a simple concept.

After downloading the app, you just have to point your phone at a math problem. It can be in a book, or it can recognize your own handwriting. The app then gives you a step-by-step explanation to solve the problem.

Combining these two things is what makes Photomath useful. WolframAlpha can solve equations, and Evernote can recognize your handwriting. But nobody thought about combining these things.

Typing an equation can be hard, so it makes a ton of sense to bridge the gap between the physical world and smartphones. Before everybody started talking about augmented reality, Photomath was already taking advantage of the system-on-a-chip in your phone.

Photomath is also capable of generating graphs and supports advanced problems, such as limits, integrations, complex numbers, etc. The app solves around 1.2 billion math problems per month.