For example, the Lehman Aggregate Bond Index contains more than 6, 000 bonds, but the Barclays iShares Lehman Aggregate Bond Fund ( AGG) contains only a little more than 100 of those bonds.

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By talking to prime brokers (the arms of banks that serve hedge funds), the authorities have also been able to monitor the aggregate level of hedge-fund exposure, and thus systemic risk.

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The first three types of fees are shown, as an aggregate total, in each mutual fund's expense ratio, and are generally reported in your 401(k)'s "summary documents" as a percentage of assets.

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