https://www.reuters.com/article/us-duolingo-ipo/duolingo-enters-major-leagues-with-6-5-billion-valuation-in-strong-debut-idUSKBN2EY2DP >(Reuters) -Language learning app Duolingo Inc notched a valuation of $6.5 billion after its shares surged nearly 40% in the company's Nasdaq debut on Wednesday, becoming the latest education technology startup to impress Wall Street.