(Bloomberg) -- Friday was a difficult day for most investors. For U.S. mutual funds with a significant share of their money in European bank stocks, it was especially brutal.

The five worst-performing major equity funds -- each of which lost about 10% -- focus on international investing and hold anywhere from 12% to 20% of their assets in bank stocks. Those shares tumbled as global markets sold off after voters in the U.K. decided to exit the European Union.

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