Global stock markets are plunging today (Aug. 24) on fears that China’s economy is in deep trouble. Among the many stocks taking a hit is Apple, down nearly 6% to $99.51 per share, but Tim Cook says he’s not worried. The Apple CEO took the unusual step of emailing CNBC’s Jim Cramer in the midst of the market-opening chaos to say the company “has continued to experience strong growth” in China, its second-largest market, during July and August.