Mark Zuckerberg has invested in , an Indian education startup that teaches kids subjects like math and science with a mobile app. Zuckerberg's philanthropic organization, the , is leading the $50 million investment along with other venture capital firms. It's the second investment Facebook's CEO has made through the Chan Zuckerberg Initiative, a company he owns with his wife, Priscilla Chan. Byju previously raised $75 million in March. "I'm optimistic about personalized learning and the difference it can make for students everywhere," on Thursday. "That's why it's a major focus of our education efforts, and why we're looking forward to working with companies like BYJU's to get these tools into the hands of more students and teachers around the world." Byju's app, which offers interactive courses and exams on a range of subjects, has been downloaded over 5.5 million times to date and boasts 250,000 annual subscribers in India. The Chan Zuckerberg Initiative previously , an African startup that teaches people how to code.