SIG Global and Lupa Systems, two private equity firms, led a $31m Series B round in Doubtnut, an edtech startup. The round was joined by Sequoia Capital, WaterBridge Ventures, Omidyar Network and ON Mauritius. The startup said it will deploy the fresh capital to add support for more language and broaden the scope of subjects it covers today. Doubtnut is also planning to introduce paid courses.