Some, such as Fidelity's Asset Manager funds and Vanguard's LifeStrategy Funds, maintain a fixed asset allocation over time.

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"We've held a substantial long position in the Mexican peso since the beginning of the year, which has done very well, and we're going to keep that for the time being simply on fundamentals and attractive valuations, " said Dagmar Dvorak, an investment manager of fixed income and currencies at Baring Asset Management in London.

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