The broad U.S. stock market has hit a rough patch the past few months, but growth stock mutual funds are so far holding up well in year-to-date and 10-year performance. Let’s see what $10,000 would do. Invested in the average growth stock mutual fund on June 30, 2005, it would have grown to $24,110 by July 27 this year, according to Morningstar Inc. data.