Tesla Inc. is assessing the risk associated with its investment portfolio. The company holds $5 billion in marketable securities, divided as follows:

• $2 billion in stocks with a standard deviation of 15%
• $1.5 billion in bonds with a standard deviation of 5%
• $1.5 billion in a diversified hedge fund with a standard deviation of 10% Assuming these securities are uncorrelated, calculate Tesla's portfolio standard deviation.