An employee who earned 3% more in their 401(k) during their working career due to this employee benefit could double their 401(k) balance at retirement.

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If Mr. Hayes is tried or enters into a plea agreement in the U.S., British prosecutors wouldn't be able to try him on similar charges under U.K. double-jeopardy rules, according to criminal-defense lawyers who aren't involved in Mr. Hayes's case.

WSJ: U.S. and U.K. in Tussle Over Trader

Special Offer: Before you make new IRA contributions or rebalance your 401(k), double check to see which Fidelity funds--and fund managers--are the best places to put your capital.

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Each DNA molecule in the body contains two long strands of chemical letters, or bases--A, T, C and G--that come together like a twisted ladder (a.k.a. the double helix).

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As they expand full throttle from a predominantly U.K. base, they could indeed double their European market share in the next five years.

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There are various ways to protect yourself from double taxation, particularly by using IRAs and 401(k)s.

FORBES: The Perverse Impact Of Double Taxation: A Helpful Flow Chart

The nine entrepreneurs featured in our slideshow--six from the U.S. and three from the U.K.--started launching businesses by the tender age of 15, and one before he broke double-digits.

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